Internet DRAFT - draft-ietf-payload-rtp-h265
draft-ietf-payload-rtp-h265
Network Working Group Y.-K. Wang
Internet Draft Qualcomm
Intended status: Standards track Y. Sanchez
Expires: May 2016 T. Schierl
Fraunhofer HHI
S. Wenger
Vidyo
M. M. Hannuksela
Nokia
November 5, 2015
RTP Payload Format for H.265/HEVC Video
draft-ietf-payload-rtp-h265-15.txt
Abstract
This memo describes an RTP payload format for the video coding
standard ITU-T Recommendation H.265 and ISO/IEC International
Standard 23008-2, both also known as High Efficiency Video Coding
(HEVC) and developed by the Joint Collaborative Team on Video
Coding (JCT-VC). The RTP payload format allows for packetization
of one or more Network Abstraction Layer (NAL) units in each RTP
packet payload, as well as fragmentation of a NAL unit into
multiple RTP packets. Furthermore, it supports transmission of
an HEVC bitstream over a single as well as multiple RTP streams.
When multiple RTP streams are used, a single or multiple
transports may be utilized. The payload format has wide
applicability in videoconferencing, Internet video streaming, and
high bit-rate entertainment-quality video, among others.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
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Table of Contents
Abstract..........................................................1
Status of this Memo...............................................1
Table of Contents.................................................3
1 Introduction....................................................5
1.1 Overview of the HEVC Codec.................................5
1.1.1 Coding-Tool Features..................................6
1.1.2 Systems and Transport Interfaces......................8
1.1.3 Parallel Processing Support..........................14
1.1.4 NAL Unit Header......................................17
1.2 Overview of the Payload Format............................18
2 Conventions....................................................19
3 Definitions and Abbreviations..................................19
3.1 Definitions...............................................19
3.1.1 Definitions from the HEVC Specification..............19
3.1.2 Definitions Specific to This Memo....................21
3.2 Abbreviations.............................................23
4 RTP Payload Format.............................................25
4.1 RTP Header Usage..........................................25
4.2 Payload Header Usage......................................27
4.3 Transmission Modes........................................28
4.4 Payload Structures........................................29
4.4.1 Single NAL Unit Packets..............................30
4.4.2 Aggregation Packets (APs)............................30
4.4.3 Fragmentation Units (FUs)............................35
4.4.4 PACI packets.........................................38
4.4.4.1 Reasons for the PACI rules (informative)........41
4.4.4.2 PACI extensions (Informative)...................42
4.5 Temporal Scalability Control Information..................43
4.6 Decoding Order Number.....................................45
5 Packetization Rules............................................47
6 De-packetization Process.......................................48
7 Payload Format Parameters......................................50
7.1 Media Type Registration...................................51
7.2 SDP Parameters............................................76
7.2.1 Mapping of Payload Type Parameters to SDP............76
7.2.2 Usage with SDP Offer/Answer Model....................78
7.2.3 Usage in Declarative Session Descriptions............87
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7.2.4 Parameter Sets Considerations........................88
7.2.5 Dependency Signaling in Multi-Stream Mode............88
8 Use with Feedback Messages.....................................89
8.1 Picture Loss Indication (PLI).............................89
8.2 Slice Loss Indication (SLI)...............................89
8.3 Reference Picture Selection Indication (RPSI).............91
8.4 Full Intra Request (FIR)..................................91
9 Security Considerations........................................92
10 Congestion Control............................................94
11 IANA Consideration............................................95
12 Acknowledgements..............................................95
13 References....................................................96
13.1 Normative References.....................................96
13.2 Informative References...................................97
14 Authors' Addresses............................................99
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1 Introduction
The High Efficiency Video Coding [HEVC], formally known as ITU-T
Recommendation H.265 and ISO/IEC International Standard 23008-2
was ratified by ITU-T in April 2013 and reportedly provides
significant coding efficiency gains over H.264 [H.264].
This memo describes an RTP payload format for HEVC. It shares
its basic design with the RTP payload formats of [RFC6184] and
[RFC6190]. With respect to design philosophy, security,
congestion control, and overall implementation complexity, it has
similar properties to those earlier payload format
specifications. This is a conscious choice, as at least RFC6184
is widely deployed and generally known in the relevant
implementer communities. Mechanisms from RFC6190 were
incorporated as HEVC version 1 supports temporal scalability.
In order to help the overlapping implementer community,
frequently only the differences between RFC6184/RFC6190 and the
HEVC payload format are highlighted in non-normative, explanatory
parts of this memo. Basic familiarity with both specifications
is assumed for those parts. However, the normative parts of this
memo do not require study of RFC6184 or RFC6190.
1.1 Overview of the HEVC Codec
H.264 and HEVC share a similar hybrid video codec design. In
this memo, we provide a very brief overview of those features of
HEVC that are in some form addressed by the payload format
specified herein. Implementers have to read and understand, and
apply the ITU-T/ISO/IEC specifications pertaining to HEVC to
arrive at interoperable, well-performing implementations.
Implementers should consider testing their design (including the
interworking between the payload format implementation and the
core video codec) using the tools provided by ITU-T/ISO/IEC; for
example, conformance bitstreams as specified in [add confermance
spec). Not doing so has historically led to badly performing and
unsecure systems.
Conceptually, both H.264 and HEVC include a video coding layer
(VCL), which is often used to refer to the coding-tool features,
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and a network abstraction layer (NAL), which is often used to
refer to the systems and transport interface aspects of the
codecs.
1.1.1 Coding-Tool Features
Similarly to earlier hybrid-video-coding-based standards,
including H.264, the following basic video coding design is
employed by HEVC. A prediction signal is first formed either by
intra or motion compensated prediction, and the residual (the
difference between the original and the prediction) is then
coded. The gains in coding efficiency are achieved by
redesigning and improving almost all parts of the codec over
earlier designs. In addition, HEVC includes several tools to
make the implementation on parallel architectures easier. Below
is a summary of HEVC coding-tool features.
Quad-tree block and transform structure
One of the major tools that contribute significantly to the
coding efficiency of HEVC is the usage of flexible coding blocks
and transforms, which are defined in a hierarchical quad-tree
manner. Unlike H.264, where the basic coding block is a
macroblock of fixed size 16x16, HEVC defines a Coding Tree Unit
(CTU) of a maximum size of 64x64. Each CTU can be divided into
smaller units in a hierarchical quad-tree manner and can
represent smaller blocks down to size 4x4. Similarly, the
transforms used in HEVC can have different sizes, starting from
4x4 and going up to 32x32. Utilizing large blocks and transforms
contribute to the major gain of HEVC, especially at high
resolutions.
Entropy coding
HEVC uses a single entropy coding engine, which is based on
Context Adaptive Binary Arithmetic Coding (CABAC) [CABAC],
whereas H.264 uses two distinct entropy coding engines. CABAC in
HEVC shares many similarities with CABAC of H.264, but contains
several improvements. Those include improvements in coding
efficiency and lowered implementation complexity, especially for
parallel architectures.
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In-loop filtering
H.264 includes an in-loop adaptive deblocking filter, where the
blocking artifacts around the transform edges in the
reconstructed picture are smoothed to improve the picture quality
and compression efficiency. In HEVC, a similar deblocking filter
is employed but with somewhat lower complexity. In addition,
pictures undergo a subsequent filtering operation called Sample
Adaptive Offset (SAO), which is a new design element in HEVC.
SAO basically adds a pixel-level offset in an adaptive manner and
usually acts as a de-ringing filter. It is observed that SAO
improves the picture quality, especially around sharp edges
contributing substantially to visual quality improvements of
HEVC.
Motion prediction and coding
There have been a number of improvements in this area that are
summarized as follows. The first category is motion merge and
advanced motion vector prediction (AMVP) modes. The motion
information of a prediction block can be inferred from the
spatially or temporally neighboring blocks. This is similar to
the DIRECT mode in H.264 but includes new aspects to incorporate
the flexible quad-tree structure and methods to improve the
parallel implementations. In addition, the motion vector
predictor can be signaled for improved efficiency. The second
category is high-precision interpolation. The interpolation
filter length is increased to 8-tap from 6-tap, which improves
the coding efficiency but also comes with increased complexity.
In addition, the interpolation filter is defined with higher
precision without any intermediate rounding operations to further
improve the coding efficiency.
Intra prediction and intra coding
Compared to 8 intra prediction modes in H.264, HEVC supports
angular intra prediction with 33 directions. This increased
flexibility improves both objective coding efficiency and visual
quality as the edges can be better predicted and ringing
artifacts around the edges can be reduced. In addition, the
reference samples are adaptively smoothed based on the prediction
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direction. To avoid contouring artifacts a new interpolative
prediction generation is included to improve the visual quality.
Furthermore, discrete sine transform (DST) is utilized instead of
traditional discrete cosine transform (DCT) for 4x4 intra
transform blocks.
Other coding-tool features
HEVC includes some tools for lossless coding and efficient screen
content coding, such as skipping the transform for certain
blocks. These tools are particularly useful for example when
streaming the user-interface of a mobile device to a large
display.
1.1.2 Systems and Transport Interfaces
HEVC inherited the basic systems and transport interfaces
designs, such as the NAL-unit-based syntax structure, the
hierarchical syntax and data unit structure from sequence-level
parameter sets, multi-picture-level or picture-level parameter
sets, slice-level header parameters, lower-level parameters, the
supplemental enhancement information (SEI) message mechanism, the
hypothetical reference decoder (HRD) based video buffering model,
and so on. In the following, a list of differences in these
aspects compared to H.264 is summarized.
Video parameter set
A new type of parameter set, called video parameter set (VPS),
was introduced. For the first (2013) version of [HEVC], the
video parameter set NAL unit is required to be available prior to
its activation, while the information contained in the video
parameter set is not necessary for operation of the decoding
process. For future HEVC extensions, such as the 3D or scalable
extensions, the video parameter set is expected to include
information necessary for operation of the decoding process, e.g.
decoding dependency or information for reference picture set
construction of enhancement layers. The VPS provides a "big
picture" of a bitstream, including what types of operation points
are provided, the profile, tier, and level of the operation
points, and some other high-level properties of the bitstream
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that can be used as the basis for session negotiation and content
selection, etc. (see Section 7.1).
Profile, tier and level
The profile, tier and level syntax structure that can be included
in both VPS and sequence parameter set (SPS) includes 12 bytes of
data to describe the entire bitstream (including all temporally
scalable layers, which are referred to as sub-layers in the HEVC
specification), and can optionally include more profile, tier and
level information pertaining to individual temporally scalable
layers. The profile indicator indicates the "best viewed as"
profile when the bitstream conforms to multiple profiles, similar
to the major brand concept in the ISO base media file format
(ISOBMFF) [ISOBMFF] and file formats derived based on ISOBMFF,
such as the 3GPP file format [3GPPFF]. The profile, tier and
level syntax structure also includes indications such as 1)
whether the bitstream is free of frame-packed content, 2) whether
the bitstream is free of interlaced source content, and 3)
whether the bitstream is free of field pictures. When the answer
is yes for both 2) and 3), the bitstream contains only frame
pictures of progressive source. Based on these indications,
clients/players without support of post-processing
functionalities for handling of frame-packed, interlaced source
content or field pictures can reject those bitstreams that
contain such pictures.
Bitstream and elementary stream
HEVC includes a definition of an elementary stream, which is new
compared to H.264. An elementary stream consists of a sequence
of one or more bitstreams. An elementary stream that consists of
two or more bitstreams has typically been formed by splicing
together two or more bitstreams (or parts thereof). When an
elementary stream contains more than one bitstream, the last NAL
unit of the last access unit of a bitstream (except the last
bitstream in the elementary stream) must contain an end of
bitstream NAL unit and the first access unit of the subsequent
bitstream must be an intra random access point (IRAP) access
unit. This IRAP access unit may be a clean random access (CRA),
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broken link access (BLA), or instantaneous decoding refresh (IDR)
access unit.
Random access support
HEVC includes signaling in the NAL unit header, through NAL unit
types, of IRAP pictures beyond IDR pictures. Three types of IRAP
pictures, namely IDR, CRA and BLA pictures are supported, wherein
IDR pictures are conventionally referred to as closed group-of-
pictures (closed-GOP) random access points, and CRA and BLA
pictures are those conventionally referred to as open-GOP random
access points. BLA pictures usually originate from splicing of
two bitstreams or part thereof at a CRA picture, e.g. during
stream switching. To enable better systems usage of IRAP
pictures, altogether six different NAL units are defined to
signal the properties of the IRAP pictures, which can be used to
better match the stream access point (SAP) types as defined in
the ISOBMFF [ISOBMFF], which are utilized for random access
support in both 3GP-DASH [3GPDASH] and MPEG DASH [MPEGDASH].
Pictures following an IRAP picture in decoding order and
preceding the IRAP picture in output order are referred to as
leading pictures associated with the IRAP picture. There are two
types of leading pictures, namely random access decodable leading
(RADL) pictures and random access skipped leading (RASL)
pictures. RADL pictures are decodable when the decoding started
at the associated IRAP picture, and RASL pictures are not
decodable when the decoding started at the associated IRAP
picture and are usually discarded. HEVC provides mechanisms to
enable the specification of conformance of bitstreams with RASL
pictures being discarded, thus to provide a standard-compliant
way to enable systems components to discard RASL pictures when
needed.
Temporal scalability support
HEVC includes an improved support of temporal scalability, by
inclusion of the signaling of TemporalId in the NAL unit header,
the restriction that pictures of a particular temporal sub-layer
cannot be used for inter prediction reference by pictures of a
lower temporal sub-layer, the sub-bitstream extraction process,
and the requirement that each sub-bitstream extraction output be
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a conforming bitstream. Media-aware network elements (MANEs) can
utilize the TemporalId in the NAL unit header for stream
adaptation purposes based on temporal scalability.
Temporal sub-layer switching support
HEVC specifies, through NAL unit types present in the NAL unit
header, the signaling of temporal sub-layer access (TSA) and
stepwise temporal sub-layer access (STSA). A TSA picture and
pictures following the TSA picture in decoding order do not use
pictures prior to the TSA picture in decoding order with
TemporalId greater than or equal to that of the TSA picture for
inter prediction reference. A TSA picture enables up-switching,
at the TSA picture, to the sub-layer containing the TSA picture
or any higher sub-layer, from the immediately lower sub-layer.
An STSA picture does not use pictures with the same TemporalId as
the STSA picture for inter prediction reference. Pictures
following an STSA picture in decoding order with the same
TemporalId as the STSA picture do not use pictures prior to the
STSA picture in decoding order with the same TemporalId as the
STSA picture for inter prediction reference. An STSA picture
enables up-switching, at the STSA picture, to the sub-layer
containing the STSA picture, from the immediately lower sub-
layer.
Sub-layer reference or non-reference pictures
The concept and signaling of reference/non-reference pictures in
HEVC are different from H.264. In H.264, if a picture may be
used by any other picture for inter prediction reference, it is a
reference picture; otherwise it is a non-reference picture, and
this is signaled by two bits in the NAL unit header. In HEVC, a
picture is called a reference picture only when it is marked as
"used for reference". In addition, the concept of sub-layer
reference picture was introduced. If a picture may be used by
another other picture with the same TemporalId for inter
prediction reference, it is a sub-layer reference picture;
otherwise it is a sub-layer non-reference picture. Whether a
picture is a sub-layer reference picture or sub-layer non-
reference picture is signaled through NAL unit type values.
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Extensibility
Besides the TemporalId in the NAL unit header, HEVC also includes
the signaling of a six-bit layer ID in the NAL unit header, which
must be equal to 0 for a single-layer bitstream. Extension
mechanisms have been included in VPS, SPS, PPS, SEI NAL unit,
slice headers, and so on. All these extension mechanisms enable
future extensions in a backward compatible manner, such that
bitstreams encoded according to potential future HEVC extensions
can be fed to then-legacy decoders (e.g. HEVC version 1 decoders)
and the then-legacy decoders can decode and output the base layer
bitstream.
Bitstream extraction
HEVC includes a bitstream extraction process as an integral part
of the overall decoding process, as well as specification of the
use of the bitstream extraction process in description of
bitstream conformance tests as part of the hypothetical reference
decoder (HRD) specification.
Reference picture management
The reference picture management of HEVC, including reference
picture marking and removal from the decoded picture buffer (DPB)
as well as reference picture list construction (RPLC), differs
from that of H.264. Instead of the sliding window plus adaptive
memory management control operation (MMCO) based reference
picture marking mechanism in H.264, HEVC specifies a reference
picture set (RPS) based reference picture management and marking
mechanism, and the RPLC is consequently based on the RPS
mechanism. A reference picture set consists of a set of
reference pictures associated with a picture, consisting of all
reference pictures that are prior to the associated picture in
decoding order, that may be used for inter prediction of the
associated picture or any picture following the associated
picture in decoding order. The reference picture set consists of
five lists of reference pictures; RefPicSetStCurrBefore,
RefPicSetStCurrAfter, RefPicSetStFoll, RefPicSetLtCurr and
RefPicSetLtFoll. RefPicSetStCurrBefore, RefPicSetStCurrAfter and
RefPicSetLtCurr contain all reference pictures that may be used
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in inter prediction of the current picture and that may be used
in inter prediction of one or more of the pictures following the
current picture in decoding order. RefPicSetStFoll and
RefPicSetLtFoll consist of all reference pictures that are not
used in inter prediction of the current picture but may be used
in inter prediction of one or more of the pictures following the
current picture in decoding order. RPS provides an "intra-coded"
signaling of the DPB status, instead of an "inter-coded"
signaling, mainly for improved error resilience. The RPLC
process in HEVC is based on the RPS, by signaling an index to an
RPS subset for each reference index; this process is simpler than
the RPLC process in H.264.
Ultra low delay support
HEVC specifies a sub-picture-level HRD operation, for support of
the so-called ultra-low delay. The mechanism specifies a
standard-compliant way to enable delay reduction below one
picture interval. Sub-picture-level coded picture buffer (CPB)
and DPB parameters may be signaled, and utilization of these
information for the derivation of CPB timing (wherein the CPB
removal time corresponds to decoding time) and DPB output timing
(display time) is specified. Decoders are allowed to operate the
HRD at the conventional access-unit-level, even when the sub-
picture-level HRD parameters are present.
New SEI messages
HEVC inherits many H.264 SEI messages with changes in syntax
and/or semantics making them applicable to HEVC. Additionally,
there are a few new SEI messages reviewed briefly in the
following paragraphs.
The display orientation SEI message informs the decoder of a
transformation that is recommended to be applied to the cropped
decoded picture prior to display, such that the pictures can be
properly displayed, e.g. in an upside-up manner.
The structure of pictures SEI message provides information on the
NAL unit types, picture order count values, and prediction
dependencies of a sequence of pictures. The SEI message can be
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used for example for concluding what impact a lost picture has on
other pictures.
The decoded picture hash SEI message provides a checksum derived
from the sample values of a decoded picture. It can be used for
detecting whether a picture was correctly received and decoded.
The active parameter sets SEI message includes the IDs of the
active video parameter set and the active sequence parameter set
and can be used to activate VPSs and SPSs. In addition, the SEI
message includes the following indications: 1) An indication of
whether "full random accessibility" is supported (when supported,
all parameter sets needed for decoding of the remaining of the
bitstream when random accessing from the beginning of the current
CVS by completely discarding all access units earlier in decoding
order are present in the remaining bitstream and all coded
pictures in the remaining bitstream can be correctly decoded); 2)
An indication of whether there is no parameter set within the
current CVS that updates another parameter set of the same type
preceding in decoding order. An update of a parameter set refers
to the use of the same parameter set ID but with some other
parameters changed. If this property is true for all CVSs in the
bitstream, then all parameter sets can be sent out-of-band before
session start.
The decoding unit information SEI message provides coded picture
buffer removal delay information for a decoding unit. The
message can be used in very-low-delay buffering operations.
The region refresh information SEI message can be used together
with the recovery point SEI message (present in both H.264 and
HEVC) for improved support of gradual decoding refresh. This
supports random access from inter-coded pictures, wherein
complete pictures can be correctly decoded or recovered after an
indicated number of pictures in output/display order.
1.1.3 Parallel Processing Support
The reportedly significantly higher encoding computational demand
of HEVC over H.264, in conjunction with the ever increasing video
resolution (both spatially and temporally) required by the
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market, led to the adoption of VCL coding tools specifically
targeted to allow for parallelization on the sub-picture level.
That is, parallelization occurs, at the minimum, at the
granularity of an integer number of CTUs. The targets for this
type of high-level parallelization are multicore CPUs and DSPs as
well as multiprocessor systems. In a system design, to be
useful, these tools require signaling support, which is provided
in Section 7 of this memo. This section provides a brief
overview of the tools available in [HEVC].
Many of the tools incorporated in HEVC were designed keeping in
mind the potential parallel implementations in multi-core/multi-
processor architectures. Specifically, for parallelization, four
picture partition strategies, as described below, are available.
Slices are segments of the bitstream that can be reconstructed
independently from other slices within the same picture (though
there may still be interdependencies through loop filtering
operations). Slices are the only tool that can be used for
parallelization that is also available, in virtually identical
form, in H.264. Slices based parallelization does not require
much inter-processor or inter-core communication (except for
inter-processor or inter-core data sharing for motion
compensation when decoding a predictively coded picture, which is
typically much heavier than inter-processor or inter-core data
sharing due to in-picture prediction), as slices are designed to
be independently decodable. However, for the same reason, slices
can require some coding overhead. Further, slices (in contrast
to some of the other tools mentioned below) also serve as the key
mechanism for bitstream partitioning to match Maximum Transfer
Unit (MTU) size requirements, due to the in-picture independence
of slices and the fact that each regular slice is encapsulated in
its own NAL unit. In many cases, the goal of parallelization and
the goal of MTU size matching can place contradicting demands to
the slice layout in a picture. The realization of this situation
led to the development of the more advanced tools mentioned
below.
Dependent slice segments allow for fragmentation of a coded slice
into fragments at CTU boundaries without breaking any in-picture
prediction mechanism. They are complementary to the
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fragmentation mechanism described in this memo in that they need
the cooperation of the encoder. As a dependent slice segment
necessarily contains an integer number of CTUs, a decoder using
multiple cores operating on CTUs can process a dependent slice
segment without communicating parts of the slice segment's
bitstream to other cores. Fragmentation, as specified in this
memo, in contrast, does not guarantee that a fragment contains an
integer number of CTUs.
In wavefront parallel processing (WPP), the picture is
partitioned into rows of CTUs. Entropy decoding and prediction
are allowed to use data from CTUs in other partitions. Parallel
processing is possible through parallel decoding of CTU rows,
where the start of the decoding of a row is delayed by two CTUs,
so to ensure that data related to a CTU above and to the right of
the subject CTU is available before the subject CTU is being
decoded. Using this staggered start (which appears like a
wavefront when represented graphically), parallelization is
possible with up to as many processors/cores as the picture
contains CTU rows.
Because in-picture prediction between neighboring CTU rows within
a picture is allowed, the required inter-processor/inter-core
communication to enable in-picture prediction can be substantial.
The WPP partitioning does not result in the creation of more NAL
units compared to when it is not applied, thus WPP cannot be used
for MTU size matching, though slices can be used in combination
for that purpose.
Tiles define horizontal and vertical boundaries that partition a
picture into tile columns and rows. The scan order of CTUs is
changed to be local within a tile (in the order of a CTU raster
scan of a tile), before decoding the top-left CTU of the next
tile in the order of tile raster scan of a picture. Similar to
slices, tiles break in-picture prediction dependencies (including
entropy decoding dependencies). However, they do not need to be
included into individual NAL units (same as WPP in this regard),
hence tiles cannot be used for MTU size matching, though slices
can be used in combination for that purpose. Each tile can be
processed by one processor/core, and the inter-processor/inter-
core communication required for in-picture prediction between
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processing units decoding neighboring tiles is limited to
conveying the shared slice header in cases a slice is spanning
more than one tile, and loop filtering related sharing of
reconstructed samples and metadata. Insofar, tiles are less
demanding in terms of inter-processor communication bandwidth
compared to WPP due to the in-picture independence between two
neighboring partitions.
1.1.4 NAL Unit Header
HEVC maintains the NAL unit concept of H.264 with modifications.
HEVC uses a two-byte NAL unit header, as shown in Figure 1. The
payload of a NAL unit refers to the NAL unit excluding the NAL
unit header.
+---------------+---------------+
|0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F| Type | LayerId | TID |
+-------------+-----------------+
Figure 1 The structure of HEVC NAL unit header
The semantics of the fields in the NAL unit header are as
specified in [HEVC] and described briefly below for convenience.
In addition to the name and size of each field, the corresponding
syntax element name in [HEVC] is also provided.
F: 1 bit
forbidden_zero_bit. Required to be zero in [HEVC]. Note that
the inclusion of this bit in the NAL unit header was to enable
transport of HEVC video over MPEG-2 transport systems
(avoidance of start code emulations) [MPEG2S]. In the context
of this memo, the value 1 may be used to indicate a syntax
violation, e.g. for a NAL unit resulted from aggregating a
number of fragmented units of a NAL unit but missing the last
fragment, as described in Section 4.4.3.
Type: 6 bits
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nal_unit_type. This field specifies the NAL unit type as
defined in Table 7-1 of [HEVC]. If the most significant bit
of this field of a NAL unit is equal to 0 (i.e. the value of
this field is less than 32), the NAL unit is a VCL NAL unit.
Otherwise, the NAL unit is a non-VCL NAL unit. For a
reference of all currently defined NAL unit types and their
semantics, please refer to Section 7.4.1 in [HEVC].
LayerId: 6 bits
nuh_layer_id. Required to be equal to zero in [HEVC]. It is
anticipated that in future scalable or 3D video coding
extensions of this specification, this syntax element will be
used to identify additional layers that may be present in the
CVS, wherein a layer may be, e.g. a spatial scalable layer, a
quality scalable layer, a texture view, or a depth view.
TID: 3 bits
nuh_temporal_id_plus1. This field specifies the temporal
identifier of the NAL unit plus 1. The value of TemporalId is
equal to TID minus 1. A TID value of 0 is illegal to ensure
that there is at least one bit in the NAL unit header equal to
1, so to enable independent considerations of start code
emulations in the NAL unit header and in the NAL unit payload
data.
1.2 Overview of the Payload Format
This payload format defines the following processes required for
transport of HEVC coded data over RTP [RFC3550]:
o Usage of RTP header with this payload format
o Packetization of HEVC coded NAL units into RTP packets using
three types of payload structures, namely single NAL unit
packet, aggregation packet, and fragment unit
o Transmission of HEVC NAL units of the same bitstream within a
single RTP stream or multiple RTP streams (within one or more
RTP sessions), where within an RTP stream transmission of NAL
units may be either non-interleaved (i.e. the transmission
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order of NAL units is the same as their decoding order) or
interleaved (i.e. the transmission order of NAL units is
different from their decoding order)
o Media type parameters to be used with the Session Description
Protocol (SDP) [RFC4566]
o A payload header extension mechanism and data structures for
enhanced support of temporal scalability based on that
extension mechanism.
2 Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14, RFC 2119 [RFC2119].
In this document, these key words will appear with that
interpretation only when in ALL CAPS. Lower case uses of these
words are not to be interpreted as carrying the RFC 2119
significance.
This specification uses the notion of setting and clearing a bit
when bit fields are handled. Setting a bit is the same as
assigning that bit the value of 1 (On). Clearing a bit is the
same as assigning that bit the value of 0 (Off).
3 Definitions and Abbreviations
3.1 Definitions
This document uses the terms and definitions of [HEVC]. Section
3.1.1 lists relevant definitions copied from [HEVC] (the April
2013 version of the H.265 specification) for convenience.
Section 3.1.2 provides definitions specific to this memo.
3.1.1 Definitions from the HEVC Specification
access unit: A set of NAL units that are associated with each
other according to a specified classification rule, are
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consecutive in decoding order, and contain exactly one coded
picture.
BLA access unit: An access unit in which the coded picture is a
BLA picture.
BLA picture: An IRAP picture for which each VCL NAL unit has
nal_unit_type equal to BLA_W_LP, BLA_W_RADL, or BLA_N_LP.
coded video sequence (CVS): A sequence of access units that
consists, in decoding order, of an IRAP access unit with
NoRaslOutputFlag equal to 1, followed by zero or more access
units that are not IRAP access units with NoRaslOutputFlag equal
to 1, including all subsequent access units up to but not
including any subsequent access unit that is an IRAP access unit
with NoRaslOutputFlag equal to 1.
Informative note: An IRAP access unit may be an IDR access
unit, a BLA access unit, or a CRA access unit. The value of
NoRaslOutputFlag is equal to 1 for each IDR access unit, each
BLA access unit, and each CRA access unit that is the first
access unit in the bitstream in decoding order, is the first
access unit that follows an end of sequence NAL unit in
decoding order, or has HandleCraAsBlaFlag equal to 1.
CRA access unit: An access unit in which the coded picture is a
CRA picture.
CRA picture: A RAP picture for which each VCL NAL unit has
nal_unit_type equal to CRA_NUT.
IDR access unit: An access unit in which the coded picture is an
IDR picture.
IDR picture: A RAP picture for which each VCL NAL unit has
nal_unit_type equal to IDR_W_RADL or IDR_N_LP.
IRAP access unit: An access unit in which the coded picture is an
IRAP picture.
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IRAP picture: A coded picture for which each VCL NAL unit has
nal_unit_type in the range of BLA_W_LP (16) to RSV_IRAP_VCL23
(23), inclusive.
layer: A set of VCL NAL units that all have a particular value of
nuh_layer_id and the associated non-VCL NAL units, or one of a
set of syntactical structures having a hierarchical relationship.
operation point: bitstream created from another bitstream by
operation of the sub-bitstream extraction process with the
another bitstream, a target highest TemporalId, and a target
layer identifier list as inputs.
random access: The act of starting the decoding process for a
bitstream at a point other than the beginning of the bitstream.
sub-layer: A temporal scalable layer of a temporal scalable
bitstream consisting of VCL NAL units with a particular value of
the TemporalId variable, and the associated non-VCL NAL units.
sub-layer representation: A subset of the bitstream consisting of
NAL units of a particular sub-layer and the lower sub-layers.
tile: A rectangular region of coding tree blocks within a
particular tile column and a particular tile row in a picture.
tile column: A rectangular region of coding tree blocks having a
height equal to the height of the picture and a width specified
by syntax elements in the picture parameter set.
tile row: A rectangular region of coding tree blocks having a
height specified by syntax elements in the picture parameter set
and a width equal to the width of the picture.
3.1.2 Definitions Specific to This Memo
dependee RTP stream: An RTP stream on which another RTP stream
depends. All RTP streams in an MRST or MRMT except for the
highest RTP stream are dependee RTP streams.
highest RTP stream: The RTP stream on which no other RTP stream
depends. The RTP stream in an SRST is the highest RTP stream.
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media aware network element (MANE): A network element, such as a
middlebox, selective forwarding unit, or application layer
gateway that is capable of parsing certain aspects of the RTP
payload headers or the RTP payload and reacting to their
contents.
Informative note: The concept of a MANE goes beyond normal
routers or gateways in that a MANE has to be aware of the
signaling (e.g. to learn about the payload type mappings of
the media streams), and in that it has to be trusted when
working with SRTP. The advantage of using MANEs is that they
allow packets to be dropped according to the needs of the
media coding. For example, if a MANE has to drop packets due
to congestion on a certain link, it can identify and remove
those packets whose elimination produces the least adverse
effect on the user experience. After dropping packets, MANEs
must rewrite RTCP packets to match the changes to the RTP
stream as specified in Section 7 of [RFC3550].
Media Transport: As used in the MRST, MRMT, and SRST definitions
below, Media Transport denotes the transport of packets over a
transport association identified by a 5-tuple (source address,
source port, destination address, destination port, transport
protocol). See also Section 2.1.13 of [I-D.ietf-avtext-rtp-
grouping-taxonomy].
Informative note: The term "bitstream" in this document is
equivalent to the term "encoded stream" in [I-D.ietf-avtext-
rtp-grouping-taxonomy].
Multiple RTP streams on a Single Transport (MRST): Multiple RTP
streams carrying a single HEVC bitstream on a Single Transport.
See also Section 3.5 of [I-D.ietf-avtext-rtp-grouping-taxonomy].
Multiple RTP streams on Multiple Transports (MRMT): Multiple RTP
streams carrying a single HEVC bitstream on Multiple Transports.
See also Section 3.5 of [I-D.ietf-avtext-rtp-grouping-taxonomy].
NAL unit decoding order: A NAL unit order that conforms to the
constraints on NAL unit order given in Section 7.4.2.4 in [HEVC].
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NAL unit output order: A NAL unit order in which NAL units of
different access units are in the output order of the decoded
pictures corresponding to the access units, as specified in
[HEVC], and in which NAL units within an access unit are in their
decoding order.
NAL-unit-like structure: A data structure that is similar to NAL
units in the sense that it also has a NAL unit header and a
payload, with a difference that the payload does not follow the
start code emulation prevention mechanism required for the NAL
unit syntax as specified in Section 7.3.1.1 of [HEVC]. Examples
NAL-unit-like structures defined in this memo are packet payloads
of AP, PACI, and FU packets.
NALU-time: The value that the RTP timestamp would have if the NAL
unit would be transported in its own RTP packet.
RTP stream: See [I-D.ietf-avtext-rtp-grouping-taxonomy]. Within
the scope of this memo, one RTP stream is utilized to transport
one or more temporal sub-layers.
Single RTP stream on a Single Transport (SRST): Single RTP
stream carrying a single HEVC bitstream on a Single (Media)
Transport. See also Section 3.5 of [I-D.ietf-avtext-rtp-
grouping-taxonomy].
transmission order: The order of packets in ascending RTP
sequence number order (in modulo arithmetic). Within an
aggregation packet, the NAL unit transmission order is the same
as the order of appearance of NAL units in the packet.
3.2 Abbreviations
AP Aggregation Packet
BLA Broken Link Access
CRA Clean Random Access
CTB Coding Tree Block
CTU Coding Tree Unit
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CVS Coded Video Sequence
DPH Decoded Picture Hash
FU Fragmentation Unit
HRD Hypothetical Reference Decoder
IDR Instantaneous Decoding Refresh
IRAP Intra Random Access Point
MANE Media Aware Network Element
MRMT Multiple RTP streams on Multiple Transports
MRST Multiple RTP streams on a Single Transport
MTU Maximum Transfer Unit
NAL Network Abstraction Layer
NALU Network Abstraction Layer Unit
PACI PAyload Content Information
PHES Payload Header Extension Structure
PPS Picture Parameter Set
RADL Random Access Decodable Leading (Picture)
RASL Random Access Skipped Leading (Picture)
RPS Reference Picture Set
SEI Supplemental Enhancement Information
SPS Sequence Parameter Set
SRST Single RTP stream on a Single Transport
STSA Step-wise Temporal Sub-layer Access
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TSA Temporal Sub-layer Access
TSCI Temporal Scalability Control Information
VCL Video Coding Layer
VPS Video Parameter Set
4 RTP Payload Format
4.1 RTP Header Usage
The format of the RTP header is specified in [RFC3550] and
reprinted in Figure 2 for convenience. This payload format uses
the fields of the header in a manner consistent with that
specification.
The RTP payload (and the settings for some RTP header bits) for
aggregation packets and fragmentation units are specified in
Sections 4.4.2 and 4.4.3, respectively.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| contributing source (CSRC) identifiers |
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 RTP header according to [RFC3550]
The RTP header information to be set according to this RTP
payload format is set as follows:
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Marker bit (M): 1 bit
Set for the last packet of the access unit, carried in the
current RTP stream. This is in line with the normal use of
the M bit in video formats to allow an efficient playout
buffer handling. When MRST or MRMT is in use, if an access
unit appears in multiple RTP streams, the marker bit is set on
each RTP stream's last packet of the access unit.
Informative note: The content of a NAL unit does not tell
whether or not the NAL unit is the last NAL unit, in
decoding order, of an access unit. An RTP sender
implementation may obtain these information from the video
encoder. If, however, the implementation cannot obtain
these information directly from the encoder, e.g. when the
bitstream was pre-encoded, and also there is no timestamp
allocated for each NAL unit, then the sender implementation
can inspect subsequent NAL units in decoding order to
determine whether or not the NAL unit is the last NAL unit
of an access unit as follows. A NAL unit is determined to
be the last NAL unit of an access unit if it is the last
NAL unit of the bitstream. A NAL unit naluX is also
determined to be the last NAL unit of an access unit if
both the following conditions are true: 1) the next VCL NAL
unit naluY in decoding order has the high-order bit of the
first byte after its NAL unit header equal to 1, and 2) all
NAL units between naluX and naluY, when present, have
nal_unit_type in the range of 32 to 35, inclusive, equal to
39, or in the ranges of 41 to 44, inclusive, or 48 to 55,
inclusive.
Payload type (PT): 7 bits
The assignment of an RTP payload type for this new packet
format is outside the scope of this document and will not be
specified here. The assignment of a payload type has to be
performed either through the profile used or in a dynamic way.
Informative note: It is not required to use different
payload type values for different RTP streams in MRST or
MRMT.
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Sequence number (SN): 16 bits
Set and used in accordance with RFC 3550 [RFC3550].
Timestamp: 32 bits
The RTP timestamp is set to the sampling timestamp of the
content. A 90 kHz clock rate MUST be used.
If the NAL unit has no timing properties of its own (e.g.
parameter set and SEI NAL units), the RTP timestamp MUST be
set to the RTP timestamp of the coded picture of the access
unit in which the NAL unit (according to Section 7.4.2.4.4 of
[HEVC]) is included.
Receivers MUST use the RTP timestamp for the display process,
even when the bitstream contains picture timing SEI messages
or decoding unit information SEI messages as specified in
[HEVC]. However, this does not mean that picture timing SEI
messages in the bitstream should be discarded, as picture
timing SEI messages may contain frame-field information that
is important in appropriately rendering interlaced video.
Synchronization source (SSRC): 32-bits
Used to identify the source of the RTP packets. When using
SRST, by definition a single SSRC is used for all parts of a
single bitstream. In MRST or MRMT, different SSRCs are used
for each RTP stream containing a subset of the sub-layers of
the single (temporally scalable) bitstream. A receiver is
required to correctly associate the set of SSRCs that are
included parts of the same bitstream.
4.2 Payload Header Usage
The first two bytes of the payload of an RTP packet are referred
to as the payload header. The payload header consists of the
same fields (F, Type, LayerId, and TID) as the NAL unit header as
shown in Section 1.1.4, irrespective of the type of the payload
structure.
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The TID value indicates (among other things) the relative
importance of an RTP packet, for example because NAL units
belonging to higher temporal sub-layers are not used for the
decoding of lower temporal sub-layers. A lower value of TID
indicates a higher importance. More important NAL units MAY be
better protected against transmission losses than less important
NAL units.
4.3 Transmission Modes
This memo enables transmission of an HEVC bitstream over
. a single RTP stream on a single Media Transport (SRST),
. multiple RTP streams over a single Media Transport (MRST),
or
. multiple RTP streams over multiple Media Transports (MRMT).
Informative Note: While this specification enables the use of
MRST within the H.265 RTP payload, the signaling of MRST within
SDP Offer/Answer is not fully specified at the time of this
writing. See [RFC5576] and [RFC5583] for what is supported
today as well as [I-D.ietf-avtcore-rtp-multi-stream] and
[I-D.ietf-mmusic-sdp-bundle-negotiation] for future directions.
When in MRMT, the dependency of one RTP stream on another RTP
stream is typically indicated as specified in [RFC5583].
[RFC5583] can also be utilized to specify dependencies within
MRST, but only if the RTP streams utilize distinct payload types.
SRST or MRST SHOULD be used for point-to-point unicast scenarios,
while MRMT SHOULD be used for point-to-multipoint multicast
scenarios where different receivers require different operation
points of the same HEVC bitstream, to improve bandwidth utilizing
efficiency.
Informative note: A multicast may degrade to a unicast after
all but one receivers have left (this is a justification of
the first "SHOULD" instead of "MUST"), and there might be
scenarios where MRMT is desirable but not possible e.g. when
IP multicast is not deployed in certain network (this is a
justification of the second "SHOULD" instead of "MUST").
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The transmission mode is indicated by the tx-mode media parameter
(see Section 7.1). If tx-mode is equal to "SRST", SRST MUST be
used. Otherwise, if tx-mode is equal to "MRST", MRST MUST be
used. Otherwise (tx-mode is equal to "MRMT"), MRMT MUST be used.
Informative note: When an RTP stream does not depend on other
RTP streams, any of SRST, MRST and MRMT may be in use for the
RTP stream.
Receivers MUST support all of SRST, MRST, and MRMT.
Informative note: The required support of MRMT by receivers
does not imply that multicast must be supported by receivers.
4.4 Payload Structures
Four different types of RTP packet payload structures are
specified. A receiver can identify the type of an RTP packet
payload through the Type field in the payload header.
The four different payload structures are as follows:
o Single NAL unit packet: Contains a single NAL unit in the
payload, and the NAL unit header of the NAL unit also serves
as the payload header. This payload structure is specified in
Section 4.4.1.
o Aggregation packet (AP): Contains more than one NAL unit
within one access unit. This payload structure is specified
in Section 4.4.2.
o Fragmentation unit (FU): Contains a subset of a single NAL
unit. This payload structure is specified in Section 4.4.3.
o PACI carrying RTP packet: Contains a payload header (that
differs from other payload headers for efficiency), a Payload
Header Extension Structure (PHES), and a PACI payload. This
payload structure is specified in Section 4.4.4.
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4.4.1 Single NAL Unit Packets
A single NAL unit packet contains exactly one NAL unit, and
consists of a payload header (denoted as PayloadHdr), a
conditional 16-bit DONL field (in network byte order), and the
NAL unit payload data (the NAL unit excluding its NAL unit
header) of the contained NAL unit, as shown in Figure 3.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PayloadHdr | DONL (conditional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| NAL unit payload data |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 The structure a single NAL unit packet
The payload header SHOULD be an exact copy of the NAL unit header
of the contained NAL unit. However, the Type (i.e.
nal_unit_type) field MAY be changed, e.g. when it is desirable to
handle a CRA picture to be a BLA picture [JCTVC-J0107].
The DONL field, when present, specifies the value of the 16 least
significant bits of the decoding order number of the contained
NAL unit. If sprop-max-don-diff is greater than 0 for any of the
RTP streams, the DONL field MUST be present, and the variable DON
for the contained NAL unit is derived as equal to the value of
the DONL field. Otherwise (sprop-max-don-diff is equal to 0 for
all the RTP streams), the DONL field MUST NOT be present.
4.4.2 Aggregation Packets (APs)
Aggregation packets (APs) are introduced to enable the reduction
of packetization overhead for small NAL units, such as most of
the non-VCL NAL units, which are often only a few octets in size.
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An AP aggregates NAL units within one access unit. Each NAL unit
to be carried in an AP is encapsulated in an aggregation unit.
NAL units aggregated in one AP are in NAL unit decoding order.
An AP consists of a payload header (denoted as PayloadHdr)
followed by two or more aggregation units, as shown in Figure 4.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PayloadHdr (Type=48) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| two or more aggregation units |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 The structure of an aggregation packet
The fields in the payload header are set as follows. The F bit
MUST be equal to 0 if the F bit of each aggregated NAL unit is
equal to zero; otherwise, it MUST be equal to 1. The Type field
MUST be equal to 48. The value of LayerId MUST be equal to the
lowest value of LayerId of all the aggregated NAL units. The
value of TID MUST be the lowest value of TID of all the
aggregated NAL units.
Informative Note: All VCL NAL units in an AP have the same TID
value since they belong to the same access unit. However, an
AP may contain non-VCL NAL units for which the TID value in
the NAL unit header may be different than the TID value of the
VCL NAL units in the same AP.
An AP MUST carry at least two aggregation units and can carry as
many aggregation units as necessary; however, the total amount of
data in an AP obviously MUST fit into an IP packet, and the size
SHOULD be chosen so that the resulting IP packet is smaller than
the MTU size so to avoid IP layer fragmentation. An AP MUST NOT
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contain Fragmentation Units (FUs) specified in Section 4.4.3.
APs MUST NOT be nested; i.e. an AP must not contain another AP.
The first aggregation unit in an AP consists of a conditional 16-
bit DONL field (in network byte order) followed by a 16-bit
unsigned size information (in network byte order) that indicates
the size of the NAL unit in bytes (excluding these two octets,
but including the NAL unit header), followed by the NAL unit
itself, including its NAL unit header, as shown in Figure 5.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: DONL (conditional) | NALU size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU size | |
+-+-+-+-+-+-+-+-+ NAL unit |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 The structure of the first aggregation unit in an AP
The DONL field, when present, specifies the value of the 16 least
significant bits of the decoding order number of the aggregated
NAL unit.
If sprop-max-don-diff is greater than 0 for any of the RTP
streams, the DONL field MUST be present in an aggregation unit
that is the first aggregation unit in an AP, and the variable DON
for the aggregated NAL unit is derived as equal to the value of
the DONL field. Otherwise (sprop-max-don-diff is equal to 0 for
all the RTP streams), the DONL field MUST NOT be present in an
aggregation unit that is the first aggregation unit in an AP.
An aggregation unit that is not the first aggregation unit in an
AP consists of a conditional 8-bit DOND field followed by a 16-
bit unsigned size information (in network byte order) that
indicates the size of the NAL unit in bytes (excluding these two
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octets, but including the NAL unit header), followed by the NAL
unit itself, including its NAL unit header, as shown in Figure 6.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: DOND (cond) | NALU size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| NAL unit |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 The structure of an aggregation unit that is not the
first aggregation unit in an AP
When present, the DOND field plus 1 specifies the difference
between the decoding order number values of the current
aggregated NAL unit and the preceding aggregated NAL unit in the
same AP.
If sprop-max-don-diff is greater than 0 for any of the RTP
streams, the DOND field MUST be present in an aggregation unit
that is not the first aggregation unit in an AP, and the variable
DON for the aggregated NAL unit is derived as equal to the DON of
the preceding aggregated NAL unit in the same AP plus the value
of the DOND field plus 1 modulo 65536. Otherwise (sprop-max-don-
diff is equal to 0 for all the RTP streams), the DOND field MUST
NOT be present in an aggregation unit that is not the first
aggregation unit in an AP, and in this case the transmission
order and decoding order of NAL units carried in the AP are the
same as the order the NAL units appear in the AP.
Figure 7 presents an example of an AP that contains two
aggregation units, labeled as 1 and 2 in the figure, without the
DONL and DOND fields being present.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PayloadHdr (Type=48) | NALU 1 Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 1 HDR | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 1 Data |
| . . . |
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . | NALU 2 Size | NALU 2 HDR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 2 HDR | |
+-+-+-+-+-+-+-+-+ NALU 2 Data |
| . . . |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 An example of an AP packet containing two aggregation
units without the DONL and DOND fields
Figure 8 presents an example of an AP that contains two
aggregation units, labeled as 1 and 2 in the figure, with the
DONL and DOND fields being present.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PayloadHdr (Type=48) | NALU 1 DONL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 1 Size | NALU 1 HDR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| NALU 1 Data . . . |
| |
+ . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | NALU 2 DOND | NALU 2 Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NALU 2 HDR | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 2 Data |
| |
| . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 An example of an AP containing two aggregation units
with the DONL and DOND fields
4.4.3 Fragmentation Units (FUs)
Fragmentation units (FUs) are introduced to enable fragmenting a
single NAL unit into multiple RTP packets, possibly without
cooperation or knowledge of the HEVC encoder. A fragment of a
NAL unit consists of an integer number of consecutive octets of
that NAL unit. Fragments of the same NAL unit MUST be sent in
consecutive order with ascending RTP sequence numbers (with no
other RTP packets within the same RTP stream being sent between
the first and last fragment).
When a NAL unit is fragmented and conveyed within FUs, it is
referred to as a fragmented NAL unit. APs MUST NOT be
fragmented. FUs MUST NOT be nested; i.e. an FU must not contain
a subset of another FU.
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The RTP timestamp of an RTP packet carrying an FU is set to the
NALU-time of the fragmented NAL unit.
An FU consists of a payload header (denoted as PayloadHdr), an FU
header of one octet, a conditional 16-bit DONL field (in network
byte order), and an FU payload, as shown in Figure 9.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PayloadHdr (Type=49) | FU header | DONL (cond) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| DONL (cond) | |
|-+-+-+-+-+-+-+-+ |
| FU payload |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9 The structure of an FU
The fields in the payload header are set as follows. The Type
field MUST be equal to 49. The fields F, LayerId, and TID MUST
be equal to the fields F, LayerId, and TID, respectively, of the
fragmented NAL unit.
The FU header consists of an S bit, an E bit, and a 6-bit FuType
field, as shown in Figure 10.
+---------------+
|0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+
|S|E| FuType |
+---------------+
Figure 10 The structure of FU header
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The semantics of the FU header fields are as follows:
S: 1 bit
When set to one, the S bit indicates the start of a fragmented
NAL unit i.e. the first byte of the FU payload is also the
first byte of the payload of the fragmented NAL unit. When
the FU payload is not the start of the fragmented NAL unit
payload, the S bit MUST be set to zero.
E: 1 bit
When set to one, the E bit indicates the end of a fragmented
NAL unit, i.e. the last byte of the payload is also the last
byte of the fragmented NAL unit. When the FU payload is not
the last fragment of a fragmented NAL unit, the E bit MUST be
set to zero.
FuType: 6 bits
The field FuType MUST be equal to the field Type of the
fragmented NAL unit.
The DONL field, when present, specifies the value of the 16 least
significant bits of the decoding order number of the fragmented
NAL unit.
If sprop-max-don-diff is greater than 0 for any of the RTP
streams, and the S bit is equal to 1, the DONL field MUST be
present in the FU, and the variable DON for the fragmented NAL
unit is derived as equal to the value of the DONL field.
Otherwise (sprop-max-don-diff is equal to 0 for all the RTP
streams, or the S bit is equal to 0), the DONL field MUST NOT be
present in the FU.
A non-fragmented NAL unit MUST NOT be transmitted in one FU; i.e.
the Start bit and End bit must not both be set to one in the same
FU header.
The FU payload consists of fragments of the payload of the
fragmented NAL unit so that if the FU payloads of consecutive
FUs, starting with an FU with the S bit equal to 1 and ending
with an FU with the E bit equal to 1, are sequentially
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concatenated, the payload of the fragmented NAL unit can be
reconstructed. The NAL unit header of the fragmented NAL unit is
not included as such in the FU payload, but rather the
information of the NAL unit header of the fragmented NAL unit is
conveyed in F, LayerId, and TID fields of the FU payload headers
of the FUs and the FuType field of the FU header of the FUs. An
FU payload MUST NOT be empty.
If an FU is lost, the receiver SHOULD discard all following
fragmentation units in transmission order corresponding to the
same fragmented NAL unit, unless the decoder in the receiver is
known to be prepared to gracefully handle incomplete NAL units.
A receiver in an endpoint or in a MANE MAY aggregate the first n-
1 fragments of a NAL unit to an (incomplete) NAL unit, even if
fragment n of that NAL unit is not received. In this case, the
forbidden_zero_bit of the NAL unit MUST be set to one to indicate
a syntax violation.
4.4.4 PACI packets
This section specifies the PACI packet structure. The basic
payload header specified in this memo is intentionally limited to
the 16 bits of the NAL unit header so to keep the packetization
overhead to a minimum. However, cases have been identified where
it is advisable to include control information in an easily
accessible position in the packet header, despite the additional
overhead. One such control information is the Temporal
Scalability Control Information as specified in Section 4.5
below. PACI packets carry this and future, similar structures.
The PACI packet structure is based on a payload header extension
mechanism that is generic and extensible to carry payload header
extensions. In this section, the focus lies on the use within
this specification. Section 4.4.4.2 below provides guidance for
the specification designers in how to employ the extension
mechanism in future specifications.
A PACI packet consists of a payload header (denoted as
PayloadHdr), for which the structure follows what is described in
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Section 4.2 above. The payload header is followed by the fields
A, cType, PHSsize, F[0..2] and Y.
Figure 11 shows a PACI packet in compliance with this memo; that
is, without any extensions.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PayloadHdr (Type=50) |A| cType | PHSsize |F0..2|Y|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Header Extension Structure (PHES) |
|=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=|
| |
| PACI payload: NAL unit |
| . . . |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11 The structure of a PACI
The fields in the payload header are set as follows. The F bit
MUST be equal to 0. The Type field MUST be equal to 50. The
value of LayerId MUST be a copy of the LayerId field of the PACI
payload NAL unit or NAL-unit-like structure. The value of TID
MUST be a copy of the TID field of the PACI payload NAL unit or
NAL-unit-like structure.
The semantics of other fields are as follows:
A: 1 bit
Copy of the F bit of the PACI payload NAL unit or NAL-unit-
like structure.
cType: 6 bits
Copy of the Type field of the PACI payload NAL unit or NAL-
unit-like structure.
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PHSsize: 5 bits
Indicates the length of the PHES field. The value is limited
to be less than or equal to 32 octets, to simplify encoder
design for MTU size matching.
F0
This field equal to 1 specifies the presence of a temporal
scalability support extension in the PHES.
F1, F2
MUST be 0, available for future extensions, see Section
4.4.4.2. Receivers compliant with this version of the HEVC
payload format MUST ignore F1=1 and/or F2=1, and also ignore
any information in the PHES indicated as present by F1=1
and/or F2=1.
Informative note: The receiver can do that by first
decoding information associated with F0=1, and then
skipping over any remaining bytes of the PHES based on the
value of PHSsize.
Y: 1 bit
MUST be 0, available for future extensions, see Section
4.4.4.2. Receivers compliant with this version of the HEVC
payload format MUST ignore Y=1, and also ignore any
information in the PHES indicated as present by Y.
PHES: variable number of octets
A variable number of octets as indicated by the value of
PHSsize.
PACI Payload
The single NAL unit packet or NAL-unit-like structure (such
as: FU or AP) to be carried, not including the first two
octets.
Informative note: The first two octets of the NAL unit or
NAL-unit-like structure carried in the PACI payload are not
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included in the PACI payload. Rather, the respective values
are copied in locations of the PayloadHdr of the RTP
packet. This design offers two advantages: first, the
overall structure of the payload header is preserved, i.e.
there is no special case of payload header structure that
needs to be implemented for PACI. Second, no additional
overhead is introduced.
A PACI payload MAY be a single NAL unit, an FU, or an AP.
PACIs MUST NOT be fragmented or aggregated. The following
subsection documents the reasons for these design choices.
4.4.4.1 Reasons for the PACI rules (informative)
A PACI cannot be fragmented. If a PACI could be fragmented, and
a fragment other than the first fragment would get lost, access
to the information in the PACI would not be possible. Therefore,
a PACI must not be fragmented. In other words, an FU must not
carry (fragments of) a PACI.
A PACI cannot be aggregated. Aggregation of PACIs is inadvisable
from a compression viewpoint, as, in many cases, several to be
aggregated NAL units would share identical PACI fields and values
which would be carried redundantly for no reason. Most, if not
all the practical effects of PACI aggregation can be achieved by
aggregating NAL units and bundling them with a PACI (see below).
Therefore, a PACI must not be aggregated. In other words, an AP
must not contain a PACI.
The payload of a PACI can be a fragment. Both middleboxes and
sending systems with inflexible (often hardware-based) encoders
occasionally find themselves in situations where a PACI and its
headers, combined, are larger than the MTU size. In such a
scenario, the middlebox or sender can fragment the NAL unit and
encapsulate the fragment in a PACI. Doing so preserves the
payload header extension information for all fragments, allowing
downstream middleboxes and the receiver to take advantage of that
information. Therefore, a sender may place a fragment into a
PACI, and a receiver must be able to handle such a PACI.
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The payload of a PACI can be an aggregation NAL unit. HEVC
bitstreams can contain unevenly sized and/or small (when compared
to the MTU size) NAL units. In order to efficiently packetize
such small NAL units, AP were introduced. The benefits of APs
are independent from the need for a payload header extension.
Therefore, a sender may place an AP into a PACI, and a receiver
must be able to handle such a PACI.
4.4.4.2 PACI extensions (Informative)
This section includes recommendations for future specification
designers on how to extent the PACI syntax to accommodate future
extensions. Obviously, designers are free to specify whatever
appears to be appropriate to them at the time of their design.
However, a lot of thought has been invested into the extension
mechanism described below, and we suggest that deviations from it
warrant a good explanation.
This memo defines only a single payload header extension
(Temporal Scalability Control Information, described below in
Section 4.5), and, therefore, only the F0 bit carries semantics.
F1 and F2 are already named (and not just marked as reserved, as
a typical video spec designer would do). They are intended to
signal two additional extensions. The Y bit allows to,
recursively, add further F and Y bits to extend the mechanism
beyond 3 possible payload header extensions. It is suggested to
define a new packet type (using a different value for Type) when
assigning the F1, F2, or Y bits different semantics than what is
suggested below.
When a Y bit is set, an 8 bit flag-extension is inserted after
the Y bit. A flag-extension consists of 7 flags F[n..n+6], and
another Y bit.
The basic PACI header already includes F0, F1, and F2.
Therefore, the Fx bits in the first flag-extensions are numbered
F3, F4, ..., F9, the F bits in the second flag-extension are
numbered F10, F11, ..., F16, and so forth. As a result, at least
3 Fx bits are always in the PACI, but the number of Fx bits (and
associated types of extensions), can be increased by setting the
next Y bit and adding an octet of flag-extensions, carrying 7
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flags and another Y bit. The size of this list of flags is
subject to the limits specified in Section 4.4.4 (32 octets for
all flag-extensions and the PHES information combined).
Each of the F bits can indicate either the presence of
information in the Payload Header Extension Structure (PHES),
described below, or a given F bit can indicate a certain
condition, without including additional information in the PHES.
When a spec developer devises a new syntax that takes advantage
of the PACI extension mechanism, he/she must follow the
constraints listed below; otherwise the extension mechanism may
break.
1) The fields added for a particular Fx bit MUST be fixed in
length and not depend on what other Fx bits are set (no
parsing dependency).
2) The Fx bits must be assigned in order.
3) An implementation that supports the n-th Fn bit for any
value of n must understand the syntax (though not
necessarily the semantics) of the fields Fk (with k < n), so
to be able to either use those bits when present, or at
least be able to skip over them.
4.5 Temporal Scalability Control Information
This section describes the single payload header extension
defined in this specification, known as Temporal Scalability
Control Information (TSCI). If, in the future, additional
payload header extensions become necessary, they could be
specified in this section of an updated version of this document,
or in their own documents.
When F0 is set to 1 in a PACI, this specifies that the PHES field
includes the TSCI fields TL0PICIDX, IrapPicID, S, and E as
follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PayloadHdr (Type=50) |A| cType | PHSsize |F0..2|Y|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TL0PICIDX | IrapPicID |S|E| RES | |
|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| .... |
| PACI payload: NAL unit |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :...OPTIONAL RTP padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12 The structure of a PACI with a PHES containing a TSCI
TL0PICIDX (8 bits)
When present, the TL0PICIDX field MUST be set to equal to
temporal_sub_layer_zero_idx as specified in Section D.3.22 of
[H.265] for the access unit containing the NAL unit in the
PACI.
IrapPicID (8 bits)
When present, the IrapPicID field MUST be set to equal to
irap_pic_id as specified in Section D.3.22 of [H.265] for the
access unit containing the NAL unit in the PACI.
S (1 bit)
The S bit MUST be set to 1 if any of the following conditions
is true and MUST be set to 0 otherwise:
o The NAL unit in the payload of the PACI is the first VCL NAL
unit, in decoding order, of a picture.
o The NAL unit in the payload of the PACI is an AP and the NAL
unit in the first contained aggregation unit is the first
VCL NAL unit, in decoding order, of a picture.
o The NAL unit in the payload of the PACI is an FU with its S
bit equal to 1 and the FU payload containing a fragment of
the first VCL NAL unit, in decoding order of a picture.
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E (1 bit)
The E bit MUST be set to 1 if any of the following conditions
is true and MUST be set to 0 otherwise:
o The NAL unit in the payload of the PACI is the last VCL NAL
unit, in decoding order, of a picture.
o The NAL unit in the payload of the PACI is an AP and the NAL
unit in the last contained aggregation unit is the last VCL
NAL unit, in decoding order, of a picture.
o The NAL unit in the payload of the PACI is an FU with its E
bit equal to 1 and the FU payload containing a fragment of
the last VCL NAL unit, in decoding order of a picture.
RES (6 bits)
MUST be equal to 0. Reserved for future extensions.
The value of PHSsize MUST be set to 3. Receivers MUST allow
other values of the fields F0, F1, F2, Y, and PHSsize, and MUST
ignore any additional fields, when present, than specified above
in the PHES.
4.6 Decoding Order Number
For each NAL unit, the variable AbsDon is derived, representing
the decoding order number that is indicative of the NAL unit
decoding order.
Let NAL unit n be the n-th NAL unit in transmission order within
an RTP stream.
If sprop-max-don-diff is equal to 0 for all the RTP streams
carrying the HEVC bitstream, AbsDon[n], the value of AbsDon for
NAL unit n, is derived as equal to n.
Otherwise (sprop-max-don-diff is greater than 0 for any of the
RTP streams), AbsDon[n] is derived as follows, where DON[n] is
the value of the variable DON for NAL unit n:
o If n is equal to 0 (i.e. NAL unit n is the very first NAL unit
in transmission order), AbsDon[0] is set equal to DON[0].
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o Otherwise (n is greater than 0), the following applies for
derivation of AbsDon[n]:
If DON[n] == DON[n-1],
AbsDon[n] = AbsDon[n-1]
If (DON[n] > DON[n-1] and DON[n] - DON[n-1] < 32768),
AbsDon[n] = AbsDon[n-1] + DON[n] - DON[n-1]
If (DON[n] < DON[n-1] and DON[n-1] - DON[n] >= 32768),
AbsDon[n] = AbsDon[n-1] + 65536 - DON[n-1] + DON[n]
If (DON[n] > DON[n-1] and DON[n] - DON[n-1] >= 32768),
AbsDon[n] = AbsDon[n-1] - (DON[n-1] + 65536 -
DON[n])
If (DON[n] < DON[n-1] and DON[n-1] - DON[n] < 32768),
AbsDon[n] = AbsDon[n-1] - (DON[n-1] - DON[n])
For any two NAL units m and n, the following applies:
o AbsDon[n] greater than AbsDon[m] indicates that NAL unit n
follows NAL unit m in NAL unit decoding order.
o When AbsDon[n] is equal to AbsDon[m], the NAL unit decoding
order of the two NAL units can be in either order.
o AbsDon[n] less than AbsDon[m] indicates that NAL unit n
precedes NAL unit m in decoding order.
Informative note: When two consecutive NAL units in the NAL
unit decoding order have different values of AbsDon, the
absolute difference between the two AbsDon values may be
greater than or equal to 1.
Informative note: There are multiple reasons to allow for the
absolute difference of the values of AbsDon for two
consecutive NAL units in the NAL unit decoding order to be
greater than one. An increment by one is not required, as at
the time of associating values of AbsDon to NAL units, it may
not be known whether all NAL units are to be delivered to the
receiver. For example, a gateway may not forward VCL NAL
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units of higher sub-layers or some SEI NAL units when there is
congestion in the network. In another example, the first
intra-coded picture of a pre-encoded clip is transmitted in
advance to ensure that it is readily available in the
receiver, and when transmitting the first intra-coded picture,
the originator does not exactly know how many NAL units will
be encoded before the first intra-coded picture of the pre-
encoded clip follows in decoding order. Thus, the values of
AbsDon for the NAL units of the first intra-coded picture of
the pre-encoded clip have to be estimated when they are
transmitted, and gaps in values of AbsDon may occur. Another
example is MRST or MRMT with sprop-max-don-diff greater than
0, where the AbsDon values must indicate cross-layer decoding
order for NAL units conveyed in all the RTP streams.
5 Packetization Rules
The following packetization rules apply:
o If sprop-max-don-diff is greater than 0 for any of the RTP
streams, the transmission order of NAL units carried in the
RTP stream MAY be different than the NAL unit decoding order
and the NAL unit output order. Otherwise (sprop-max-don-diff
is equal to 0 for all the RTP streams), the transmission order
of NAL units carried in the RTP stream MUST be the same as the
NAL unit decoding order, and, when tx-mode is equal to "MRST"
or "MRMT", MUST also be the same as the NAL unit output order.
o A NAL unit of a small size SHOULD be encapsulated in an
aggregation packet together with one or more other NAL units
in order to avoid the unnecessary packetization overhead for
small NAL units. For example, non-VCL NAL units such as
access unit delimiters, parameter sets, or SEI NAL units are
typically small and can often be aggregated with VCL NAL units
without violating MTU size constraints.
o Each non-VCL NAL unit SHOULD, when possible from an MTU size
match viewpoint, be encapsulated in an aggregation packet
together with its associated VCL NAL unit, as typically a non-
VCL NAL unit would be meaningless without the associated VCL
NAL unit being available.
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o For carrying exactly one NAL unit in an RTP packet, a single
NAL unit packet MUST be used.
6 De-packetization Process
The general concept behind de-packetization is to get the NAL
units out of the RTP packets in an RTP stream and all RTP streams
the RTP stream depends on, if any, and pass them to the decoder
in the NAL unit decoding order.
The de-packetization process is implementation dependent.
Therefore, the following description should be seen as an example
of a suitable implementation. Other schemes may be used as well
as long as the output for the same input is the same as the
process described below. The output is the same when the set of
output NAL units and their order are both identical.
Optimizations relative to the described algorithms are possible.
All normal RTP mechanisms related to buffer management apply. In
particular, duplicated or outdated RTP packets (as indicated by
the RTP sequences number and the RTP timestamp) are removed. To
determine the exact time for decoding, factors such as a possible
intentional delay to allow for proper inter-stream
synchronization must be factored in.
NAL units with NAL unit type values in the range of 0 to 47,
inclusive may be passed to the decoder. NAL-unit-like structures
with NAL unit type values in the range of 48 to 63, inclusive,
MUST NOT be passed to the decoder.
The receiver includes a receiver buffer, which is used to
compensate for transmission delay jitter within individual RTP
streams and across RTP streams, to reorder NAL units from
transmission order to the NAL unit decoding order, and to recover
the NAL unit decoding order in MRST or MRMT, when applicable. In
this section, the receiver operation is described under the
assumption that there is no transmission delay jitter within an
RTP stream and across RTP streams. To make a difference from a
practical receiver buffer that is also used for compensation of
transmission delay jitter, the receiver buffer is here after
called the de-packetization buffer in this section. Receivers
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should also prepare for transmission delay jitter; i.e. either
reserve separate buffers for transmission delay jitter buffering
and de-packetization buffering or use a receiver buffer for both
transmission delay jitter and de-packetization. Moreover,
receivers should take transmission delay jitter into account in
the buffering operation; e.g. by additional initial buffering
before starting of decoding and playback.
When sprop-max-don-diff is equal to 0 for all the received RTP
streams, the de-packetization buffer size is zero bytes and the
process described in the remainder of this paragraph applies.
When there is only one RTP stream received, the NAL units carried
in the single RTP stream are directly passed to the decoder in
their transmission order, which is identical to their decoding
order. When there is more than one RTP stream received, the NAL
units carried in the multiple RTP streams are passed to the
decoder in their NTP timestamp order. When there are several NAL
units of different RTP streams with the same NTP timestamp, the
order to pass them to the decoder is their dependency order,
where NAL units of a dependee RTP stream are passed to the
decoder prior to the NAL units of the dependent RTP stream. When
there are several NAL units of the same RTP stream with the same
NTP timestamp, the order to pass them to the decoder is their
transmission order.
Informative note: The mapping between RTP and NTP
timestamps is conveyed in RTCP SR packets. In addition,
the mechanisms for faster media timestamp synchronization
discussed in [RFC6051] may be used to speed up the
acquisition of the RTP-to-wall-clock mapping.
When sprop-max-don-diff is greater than 0 for any the received
RTP streams, the process described in the remainder of this
section applies.
There are two buffering states in the receiver: initial buffering
and buffering while playing. Initial buffering starts when the
reception is initialized. After initial buffering, decoding and
playback are started, and the buffering-while-playing mode is
used.
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Regardless of the buffering state, the receiver stores incoming
NAL units, in reception order, into the de-packetization buffer.
NAL units carried in RTP packets are stored in the de-
packetization buffer individually, and the value of AbsDon is
calculated and stored for each NAL unit. When MRST or MRMT is in
use, NAL units of all RTP streams of a bitstream are stored in
the same de-packetization buffer. When NAL units carried in any
two RTP streams are available to be placed into the de-
packetization buffer, those NAL units carried in the RTP stream
that is lower in the dependency tree are placed into the buffer
first. For example, if RTP stream A depends on RTP stream B,
then NAL units carried in RTP stream B are placed into the buffer
first.
Initial buffering lasts until condition A (the difference between
the greatest and smallest AbsDon values of the NAL units in the
de-packetization buffer is greater than or equal to the value of
sprop-max-don-diff of the highest RTP stream) or condition B (the
number of NAL units in the de-packetization buffer is greater
than the value of sprop-depack-buf-nalus) is true.
After initial buffering, whenever condition A or condition B is
true, the following operation is repeatedly applied until both
condition A and condition B become false:
o The NAL unit in the de-packetization buffer with the smallest
value of AbsDon is removed from the de-packetization buffer
and passed to the decoder.
When no more NAL units are flowing into the de-packetization
buffer, all NAL units remaining in the de-packetization buffer
are removed from the buffer and passed to the decoder in the
order of increasing AbsDon values.
7 Payload Format Parameters
This section specifies the parameters that MAY be used to select
optional features of the payload format and certain features or
properties of the bitstream or the RTP stream. The parameters
are specified here as part of the media type registration for the
HEVC codec. A mapping of the parameters into the Session
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Description Protocol (SDP) [RFC4566] is also provided for
applications that use SDP. Equivalent parameters could be
defined elsewhere for use with control protocols that do not use
SDP.
7.1 Media Type Registration
The media subtype for the HEVC codec is allocated from the IETF
tree.
The receiver MUST ignore any unrecognized parameter.
Media Type name: video
Media subtype name: H265
Required parameters: none
OPTIONAL parameters:
profile-space, tier-flag, profile-id, profile-compatibility-
indicator, interop-constraints, and level-id:
These parameters indicate the profile, tier, default level,
and some constraints of the bitstream carried by the RTP
stream and all RTP streams the RTP stream depends on, or a
specific set of the profile, tier, default level, and some
constraints the receiver supports.
The profile and some constraints are indicated collectively
by profile-space, profile-id, profile-compatibility-
indicator, and interop-constraints. The profile specifies
the subset of coding tools that may have been used to
generate the bitstream or that the receiver supports.
Informative note: There are 32 values of profile-id, and
there are 32 flags in profile-compatibility-indicator,
each flag corresponding to one value of profile-id.
According to HEVC version 1 in [HEVC], when more than
one of the 32 flags is set for a bitstream, the
bitstream would comply with all the profiles
corresponding to the set flags. However, in a draft of
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HEVC version 2 in [HEVC draft v2], subclause A.3.5, 19
Format Range Extensions profiles have been specified,
all using the same value of profile-id (4),
differentiated by some of the 48 bits in interop-
constraints - this (rather unexpected way of profile
signalling) means that one of the 32 flags may
correspond to multiple profiles. To be able to support
whatever HEVC extension profile that might be specified
and indicated using profile-space, profile-id, profile-
compatibility-indicator, and interop-constraints in the
future, it would be safe to require symmetric use of
these parameters in SDP offer/answer unless recv-sub-
layer-id is included in the SDP answer for choosing one
of the sub-layers offered.
The tier is indicated by tier-flag. The default level is
indicated by level-id. The tier and the default level
specify the limits on values of syntax elements or
arithmetic combinations of values of syntax elements that
are followed when generating the bitstream or that the
receiver supports.
A set of profile-space, tier-flag, profile-id, profile-
compatibility-indicator, interop-constraints, and level-id
parameters ptlA is said to be consistent with another set
of these parameters ptlB if any decoder that conforms to
the profile, tier, level, and constraints indicated by ptlB
can decode any bitstream that conforms to the profile,
tier, level, and constraints indicated by ptlA.
In SDP offer/answer, when the SDP answer does not include
the recv-sub-layer-id parameter that is less than the
sprop-sub-layer-id parameter in the SDP offer, the
following applies:
o The profile-space, tier-flag, profile-id, profile-
compatibility-indicator, and interop-constraints
parameters MUST be used symmetrically, i.e. the value
of each of these parameters in the offer MUST be the
same as that in the answer, either explicitly
signalled or implicitly inferred.
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o The level-id parameter is changeable as long as the
highest level indicated by the answer is either equal
to or lower than that in the offer. Note that the
highest level is indicated by level-id and max-recv-
level-id together.
In SDP offer/answer, when the SDP answer does include the
recv-sub-layer-id parameter that is less than the sprop-
sub-layer-id parameter in the SDP offer, the set of
profile-space, tier-flag, profile-id, profile-
compatibility-indicator, interop-constraints, and level-id
parameters included in the answer MUST be consistent with
that for the chosen sub-layer representation as indicated
in the SDP offer, with the exception that the level-id
parameter in the SDP answer is changable as long as the
highest level indicated by the answer is either lower than
or equal to that in the offer.
More specifications of these parameters, including how they
relate to the values of the profile, tier, and level syntax
elements specified in [HEVC] are provided below.
profile-space, profile-id:
The value of profile-space MUST be in the range of 0 to 3,
inclusive. The value of profile-id MUST be in the range of
0 to 31, inclusive.
When profile-space is not present, a value of 0 MUST be
inferred. When profile-id is not present, a value of 1
(i.e. the Main profile) MUST be inferred.
When used to indicate properties of a bitstream, profile-
space and profile-id are derived from the profile, tier,
and level syntax elements in SPS or VPS NAL units as
follows, where general_profile_space, general_profile_idc,
sub_layer_profile_space[j], and sub_layer_profile_idc[j]
are specified in [HEVC]:
If the RTP stream is the highest RTP stream, the
following applies:
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o profile_space = general_profile_space
o profile_id = general_profile_idc
Otherwise (the RTP stream is a dependee RTP stream), the
following applies, with j being the value of the sprop-
sub-layer-id parameter:
o profile_space = sub_layer_profile_space[j]
o profile_id = sub_layer_profile_idc[j]
tier-flag, level-id:
The value of tier-flag MUST be in the range of 0 to 1,
inclusive. The value of level-id MUST be in the range of 0
to 255, inclusive.
If the tier-flag and level-id parameters are used to
indicate properties of a bitstream, they indicate the tier
and the highest level the bitstream complies with.
If the tier-flag and level-id parameters are used for
capability exchange, the following applies. If max-recv-
level-id is not present, the default level defined by
level-id indicates the highest level the codec wishes to
support. Otherwise, max-recv-level-id indicates the
highest level the codec supports for receiving. For either
receiving or sending, all levels that are lower than the
highest level supported MUST also be supported.
If no tier-flag is present, a value of 0 MUST be inferred
and if no level-id is present, a value of 93 (i.e. level
3.1) MUST be inferred.
When used to indicate properties of a bitstream, the tier-
flag and level-id parameters are derived from the profile,
tier, and level syntax elements in SPS or VPS NAL units as
follows, where general_tier_flag, general_level_idc,
sub_layer_tier_flag[j], and sub_layer_level_idc[j] are
specified in [HEVC]:
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If the RTP stream is the highest RTP stream, the
following applies:
o tier-flag = general_tier_flag
o level-id = general_level_idc
Otherwise (the RTP stream is a dependee RTP stream), the
following applies, with j being the value of the sprop-
sub-layer-id parameter:
o tier-flag = sub_layer_tier_flag[j]
o level-id = sub_layer_level_idc[j]
interop-constraints:
A base16 [RFC4648] (hexadecimal) representation of six
bytes of data, consisting of progressive_source_flag,
interlaced_source_flag, non_packed_constraint_flag,
frame_only_constraint_flag, and reserved_zero_44bits.
If the interop-constraints parameter is not present, the
following MUST be inferred:
o progressive_source_flag = 1
o interlaced_source_flag = 0
o non_packed_constraint_flag = 1
o frame_only_constraint_flag = 1
o reserved_zero_44bits = 0
When the interop-constraints parameter is used to indicate
properties of a bitstream, the following applies, where
general_progressive_source_flag,
general_interlaced_source_flag,
general_non_packed_constraint_flag,
general_non_packed_constraint_flag,
general_frame_only_constraint_flag,
general_reserved_zero_44bits,
sub_layer_progressive_source_flag[j],
sub_layer_interlaced_source_flag[j],
sub_layer_non_packed_constraint_flag[j],
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sub_layer_frame_only_constraint_flag[j], and
sub_layer_reserved_zero_44bits[j] are specified in [HEVC]:
If the RTP stream is the highest RTP stream, the
following applies:
o progressive_source_flag =
general_progressive_source_flag
o interlaced_source_flag =
general_interlaced_source_flag
o non_packed_constraint_flag =
general_non_packed_constraint_flag
o frame_only_constraint_flag =
general_frame_only_constraint_flag
o reserved_zero_44bits = general_reserved_zero_44bits
Otherwise (the RTP stream is a dependee RTP stream), the
following applies, with j being the value of the sprop-
sub-layer-id parameter:
o progressive_source_flag =
sub_layer_progressive_source_flag[j]
o interlaced_source_flag =
sub_layer_interlaced_source_flag[j]
o non_packed_constraint_flag =
sub_layer_non_packed_constraint_flag[j]
o frame_only_constraint_flag =
sub_layer_frame_only_constraint_flag[j]
o reserved_zero_44bits =
sub_layer_reserved_zero_44bits[j]
Using interop-constraints for capability exchange results
in a requirement on any bitstream to be compliant with the
interop-constraints.
profile-compatibility-indicator:
A base16 [RFC4648] representation of four bytes of data.
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When profile-compatibility-indicator is used to indicate
properties of a bitstream, the following applies, where
general_profile_compatibility_flag[j] and
sub_layer_profile_compatibility_flag[i][j] are specified in
[HEVC]:
The profile-compatibility-indicator in this case
indicates additional profiles to the profile defined by
profile_space, profile_id, and interop-constraints the
bitstream conforms to. A decoder that conforms to any
of all the profiles the bitstream conforms to would be
capable of decoding the bitstream. These additional
profiles are defined by profile-space, each set bit of
profile-compatibility-indicator, and interop-
constraints.
If the RTP stream is the highest RTP stream, the
following applies for each value of j in the range of 0
to 31, inclusive:
o bit j of profile-compatibility-indicator =
general_profile_compatibility_flag[j]
Otherwise (the RTP stream is a dependee RTP stream), the
following applies for i equal to sprop-sub-layer-id and
for each value of j in the range of 0 to 31, inclusive:
o bit j of profile-compatibility-indicator =
sub_layer_profile_compatibility_flag[i][j]
Using profile-compatibility-indicator for capability
exchange results in a requirement on any bitstream to be
compliant with the profile-compatibility-indicator. This
is intended to handle cases where any future HEVC profile
is defined as an intersection of two or more profiles.
If this parameter is not present, this parameter defaults
to the following: bit j, with j equal to profile-id, of
profile-compatibility-indicator is inferred to be equal to
1, and all other bits are inferred to be equal to 0.
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sprop-sub-layer-id:
This parameter MAY be used to indicate the highest allowed
value of TID in the bitstream. When not present, the value
of sprop-sub-layer-id is inferred to be equal to 6.
The value of sprop-sub-layer-id MUST be in the range of 0
to 6, inclusive.
recv-sub-layer-id:
This parameter MAY be used to signal a receiver's choice of
the offered or declared sub-layer representations in the
sprop-vps. The value of recv-sub-layer-id indicates the
TID of the highest sub-layer of the bitstream that a
receiver supports. When not present, the value of recv-
sub-layer-id is inferred to be equal to the value of the
sprop-sub-layer-id parameter in the SDP offer.
The value of recv-sub-layer-id MUST be in the range of 0 to
6, inclusive.
max-recv-level-id:
This parameter MAY be used to indicate the highest level a
receiver supports. The highest level the receiver supports
is equal to the value of max-recv-level-id divided by 30.
The value of max-recv-level-id MUST be in the range of 0
to 255, inclusive.
When max-recv-level-id is not present, the value is
inferred to be equal to level-id.
max-recv-level-id MUST NOT be present when the highest
level the receiver supports is not higher than the default
level.
tx-mode:
This parameter indicates whether the transmission mode is
SRST, MRST, or MRMT.
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The value of tx-mode MUST be equal to "SRST", "MRST" or
"MRMT". When not present, the value of tx-mode is inferred
to be equal to "SRST".
If the value is equal to "MRST", MRST MUST be in use.
Otherwise, if the value is equal to "MRMT", MRMT MUST be in
use. Otherwise (the value is equal to "SRST"), SRST MUST
be in use.
The value of tx-mode MUST be equal to "MRST" for all RTP
streams in an MRST.
The value of tx-mode MUST be equal to "MRMT" for all RTP
streams in an MRMT.
sprop-vps:
This parameter MAY be used to convey any video parameter
set NAL unit of the bitstream for out-of-band transmission
of video parameter sets. The parameter MAY also be used
for capability exchange and to indicate sub-stream
characteristics (i.e. properties of sub-layer
representations as defined in [HEVC]). The value of the
parameter is a comma-separated (',') list of base64
[RFC4648] representations of the video parameter set NAL
units as specified in Section 7.3.2.1 of [HEVC].
The sprop-vps parameter MAY contain one or more than one
video parameter set NAL unit. However, all other video
parameter sets contained in the sprop-vps parameter MUST be
consistent with the first video parameter set in the sprop-
vps parameter. A video parameter set vpsB is said to be
consistent with another video parameter set vpsA if any
decoder that conforms to the profile, tier, level, and
constraints indicated by the 12 bytes of data starting from
the syntax element general_profile_space to the syntax
element general_level_id, inclusive, in the first
profile_tier_level( ) syntax structure in vpsA can decode
any bitstream that conforms to the profile, tier, level,
and constraints indicated by the 12 bytes of data starting
from the syntax element general_profile_space to the syntax
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element general_level_id, inclusive, in the first
profile_tier_level( ) syntax structure in vpsB.
sprop-sps:
This parameter MAY be used to convey sequence parameter set
NAL units of the bitstream for out-of-band transmission of
sequence parameter sets. The value of the parameter is a
comma-separated (',') list of base64 [RFC4648]
representations of the sequence parameter set NAL units as
specified in Section 7.3.2.2 of [HEVC].
sprop-pps:
This parameter MAY be used to convey picture parameter set
NAL units of the bitstream for out-of-band transmission of
picture parameter sets. The value of the parameter is a
comma-separated (',') list of base64 [RFC4648]
representations of the picture parameter set NAL units as
specified in Section 7.3.2.3 of [HEVC].
sprop-sei:
This parameter MAY be used to convey one or more SEI
messages that describe bitstream characteristics. When
present, a decoder can rely on the bitstream
characteristics that are described in the SEI messages for
the entire duration of the session, independently from the
persistence scopes of the SEI messages as specified in
[HEVC].
The value of the parameter is a comma-separated (',') list
of base64 [RFC4648] representations of SEI NAL units as
specified in Section 7.3.2.4 of [HEVC].
Informative note: Intentionally, no list of applicable
or inapplicable SEI messages is specified here.
Conveying certain SEI messages in sprop-sei may be
sensible in some application scenarios and meaningless
in others. However, a few examples are described below:
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1) In an environment where the bitstream was created
from film-based source material, and no splicing is
going to occur during the lifetime of the session,
the film grain characteristics SEI message or the
tone mapping information SEI message are likely
meaningful, and sending them in sprop-sei rather than
in the bitstream at each entry point may help saving
bits and allows to configure the renderer only once,
avoiding unwanted artifacts.
2) The structure of pictures information SEI message in
sprop-sei can be used to inform a decoder of
information on the NAL unit types, picture order
count values, and prediction dependencies of a
sequence of pictures. Having such knowledge can be
helpful for error recovery.
3) Examples for SEI messages that would be meaningless
to be conveyed in sprop-sei include the decoded
picture hash SEI message (it is close to impossible
that all decoded pictures have the same hash-tag),
the display orientation SEI message when the device
is a handheld device (as the display orientation may
change when the handheld device is turned around), or
the filler payload SEI message (as there is no point
in just having more bits in SDP).
max-lsr, max-lps, max-cpb, max-dpb, max-br, max-tr, max-tc:
These parameters MAY be used to signal the capabilities of
a receiver implementation. These parameters MUST NOT be
used for any other purpose. The highest level (specified
by max-recv-level-id) MUST be the highest that the receiver
is fully capable of supporting. max-lsr, max-lps, max-cpb,
max-dpb, max-br, max-tr, and max-tc MAY be used to indicate
capabilities of the receiver that extend the required
capabilities of the highest level, as specified below.
When more than one parameter from the set (max-lsr, max-
lps, max-cpb, max-dpb, max-br, max-tr, max-tc) is present,
the receiver MUST support all signaled capabilities
simultaneously. For example, if both max-lsr and max-br
are present, the highest level with the extension of both
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the picture rate and bitrate is supported. That is, the
receiver is able to decode bitstreams in which the luma
sample rate is up to max-lsr (inclusive), the bitrate is up
to max-br (inclusive), the coded picture buffer size is
derived as specified in the semantics of the max-br
parameter below, and the other properties comply with the
highest level specified by max-recv-level-id.
Informative note: When the OPTIONAL media type
parameters are used to signal the properties of a
bitstream, and max-lsr, max-lps, max-cpb, max-dpb, max-
br, max-tr, and max-tc are not present, the values of
profile-space, tier-flag, profile-id, profile-
compatibility-indicator, interop-constraints, and level-
id must always be such that the bitstream complies fully
with the specified profile, tier, and level.
max-lsr:
The value of max-lsr is an integer indicating the maximum
processing rate in units of luma samples per second. The
max-lsr parameter signals that the receiver is capable of
decoding video at a higher rate than is required by the
highest level.
When max-lsr is signaled, the receiver MUST be able to
decode bitstreams that conform to the highest level, with
the exception that the MaxLumaSR value in Table A-2 of
[HEVC] for the highest level is replaced with the value of
max-lsr. Senders MAY use this knowledge to send pictures
of a given size at a higher picture rate than is indicated
in the highest level.
When not present, the value of max-lsr is inferred to be
equal to the value of MaxLumaSR given in Table A-2 of
[HEVC] for the highest level.
The value of max-lsr MUST be in the range of MaxLumaSR to
16 * MaxLumaSR, inclusive, where MaxLumaSR is given in
Table A-2 of [HEVC] for the highest level.
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max-lps:
The value of max-lps is an integer indicating the maximum
picture size in units of luma samples. The max-lps
parameter signals that the receiver is capable of decoding
larger picture sizes than are required by the highest
level. When max-lps is signaled, the receiver MUST be able
to decode bitstreams that conform to the highest level,
with the exception that the MaxLumaPS value in Table A-1 of
[HEVC] for the highest level is replaced with the value of
max-lps. Senders MAY use this knowledge to send larger
pictures at a proportionally lower picture rate than is
indicated in the highest level.
When not present, the value of max-lps is inferred to be
equal to the value of MaxLumaPS given in Table A-1 of
[HEVC] for the highest level.
The value of max-lps MUST be in the range of MaxLumaPS to
16 * MaxLumaPS, inclusive, where MaxLumaPS is given in
Table A-1 of [HEVC] for the highest level.
max-cpb:
The value of max-cpb is an integer indicating the maximum
coded picture buffer size in units of CpbBrVclFactor bits
for the VCL HRD parameters and in units of CpbBrNalFactor
bits for the NAL HRD parameters, where CpbBrVclFactor and
CpbBrNalFactor are defined in Section A.4 of [HEVC]. The
max-cpb parameter signals that the receiver has more memory
than the minimum amount of coded picture buffer memory
required by the highest level. When max-cpb is signaled,
the receiver MUST be able to decode bitstreams that conform
to the highest level, with the exception that the MaxCPB
value in Table A-1 of [HEVC] for the highest level is
replaced with the value of max-cpb. Senders MAY use this
knowledge to construct coded bitstreams with greater
variation of bitrate than can be achieved with the MaxCPB
value in Table A-1 of [HEVC].
When not present, the value of max-cpb is inferred to be
equal to the value of MaxCPB given in Table A-1 of [HEVC]
for the highest level.
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The value of max-cpb MUST be in the range of MaxCPB to
16 * MaxCPB, inclusive, where MaxLumaCPB is given in Table
A-1 of [HEVC] for the highest level.
Informative note: The coded picture buffer is used in
the hypothetical reference decoder (Annex C of HEVC).
The use of the hypothetical reference decoder is
recommended in HEVC encoders to verify that the produced
bitstream conforms to the standard and to control the
output bitrate. Thus, the coded picture buffer is
conceptually independent of any other potential buffers
in the receiver, including de-packetization and de-
jitter buffers. The coded picture buffer need not be
implemented in decoders as specified in Annex C of HEVC,
but rather standard-compliant decoders can have any
buffering arrangements provided that they can decode
standard-compliant bitstreams. Thus, in practice, the
input buffer for a video decoder can be integrated with
de-packetization and de-jitter buffers of the receiver.
max-dpb:
The value of max-dpb is an integer indicating the maximum
decoded picture buffer size in units decoded pictures at
the MaxLumaPS for the highest level, i.e. the number of
decoded pictures at the maximum picture size defined by the
highest level. The value of max-dpb MUST be in the range
of 1 to 16, respectively. The max-dpb parameter signals
that the receiver has more memory than the minimum amount
of decoded picture buffer memory required by default, which
is MaxDpbPicBuf as defined in [HEVC] (equal to 6). When
max-dpb is signaled, the receiver MUST be able to decode
bitstreams that conform to the highest level, with the
exception that the MaxDpbPicBuff value defined in [HEVC] as
6 is replaced with the value of max-dpb. Consequently, a
receiver that signals max-dpb MUST be capable of storing
the following number of decoded pictures (MaxDpbSize) in
its decoded picture buffer:
if( PicSizeInSamplesY <= ( MaxLumaPS >> 2 ) )
MaxDpbSize = Min( 4 * max-dpb, 16 )
else if ( PicSizeInSamplesY <= ( MaxLumaPS >> 1 ) )
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MaxDpbSize = Min( 2 * max-dpb, 16 )
else if ( PicSizeInSamplesY <= ( ( 3 * MaxLumaPS ) >> 2
) )
MaxDpbSize = Min( (4 * max-dpb) / 3, 16 )
else
MaxDpbSize = max-dpb
Wherein MaxLumaPS given in Table A-1 of [HEVC] for the
highest level and PicSizeInSamplesY is the current size of
each decoded picture in units of luma samples as defined in
[HEVC].
The value of max-dpb MUST be greater than or equal to the
value of MaxDpbPicBuf (i.e. 6) as defined in [HEVC].
Senders MAY use this knowledge to construct coded
bitstreams with improved compression.
When not present, the value of max-dpb is inferred to be
equal to the value of MaxDpbPicBuf (i.e. 6) as defined in
[HEVC].
Informative note: This parameter was added primarily to
complement a similar codepoint in the ITU-T
Recommendation H.245, so as to facilitate signaling
gateway designs. The decoded picture buffer stores
reconstructed samples. There is no relationship between
the size of the decoded picture buffer and the buffers
used in RTP, especially de-packetization and de-jitter
buffers.
max-br:
The value of max-br is an integer indicating the maximum
video bitrate in units of CpbBrVclFactor bits per second
for the VCL HRD parameters and in units of CpbBrNalFactor
bits per second for the NAL HRD parameters, where
CpbBrVclFactor and CpbBrNalFactor are defined in Section
A.4 of [HEVC].
The max-br parameter signals that the video decoder of the
receiver is capable of decoding video at a higher bitrate
than is required by the highest level.
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When max-br is signaled, the video codec of the receiver
MUST be able to decode bitstreams that conform to the
highest level, with the following exceptions in the limits
specified by the highest level:
o The value of max-br replaces the MaxBR value in Table A-
2 of [HEVC] for the highest level.
o When the max-cpb parameter is not present, the result of
the following formula replaces the value of MaxCPB in
Table A-1 of [HEVC]:
(MaxCPB of the highest level) * max-br / (MaxBR of
the highest level)
For example, if a receiver signals capability for Main
profile Level 2 with max-br equal to 2000, this indicates a
maximum video bitrate of 2000 kbits/sec for VCL HRD
parameters, a maximum video bitrate of 2200 kbits/sec for
NAL HRD parameters, and a CPB size of 2000000 bits (2000000
/ 1500000 * 1500000).
Senders MAY use this knowledge to send higher bitrate video
as allowed in the level definition of Annex A of HEVC to
achieve improved video quality.
When not present, the value of max-br is inferred to be
equal to the value of MaxBR given in Table A-2 of [HEVC]
for the highest level.
The value of max-br MUST be in the range of MaxBR to
16 * MaxBR, inclusive, where MaxBR is given in Table A-2 of
[HEVC] for the highest level.
Informative note: This parameter was added primarily to
complement a similar codepoint in the ITU-T
Recommendation H.245, so as to facilitate signaling
gateway designs. The assumption that the network is
capable of handling such bitrates at any given time
cannot be made from the value of this parameter. In
particular, no conclusion can be drawn that the signaled
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bitrate is possible under congestion control
constraints.
max-tr:
The value of max-tr is an integer indication the maximum
number of tile rows. The max-tr parameter signals that the
receiver is capable of decoding video with a larger number
of tile rows than the value allowed by the highest level.
When max-tr is signaled, the receiver MUST be able to
decode bitstreams that conform to the highest level, with
the exception that the MaxTileRows value in Table A-1 of
[HEVC] for the highest level is replaced with the value of
max-tr.
Senders MAY use this knowledge to send pictures utilizing a
larger number of tile rows than the value allowed by the
highest level.
When not present, the value of max-tr is inferred to be
equal to the value of MaxTileRows given in Table A-1 of
[HEVC] for the highest level.
The value of max-tr MUST be in the range of MaxTileRows to
16 * MaxTileRows, inclusive, where MaxTileRows is given in
Table A-1 of [HEVC] for the highest level.
max-tc:
The value of max-tc is an integer indication the maximum
number of tile columns. The max-tc parameter signals that
the receiver is capable of decoding video with a larger
number of tile columns than the value allowed by the
highest level.
When max-tc is signaled, the receiver MUST be able to
decode bitstreams that conform to the highest level, with
the exception that the MaxTileCols value in Table A-1 of
[HEVC] for the highest level is replaced with the value of
max-tc.
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Senders MAY use this knowledge to send pictures utilizing a
larger number of tile columns than the value allowed by the
highest level.
When not present, the value of max-tc is inferred to be
equal to the value of MaxTileCols given in Table A-1 of
[HEVC] for the highest level.
The value of max-tc MUST be in the range of MaxTileCols to
16 * MaxTileCols, inclusive, where MaxTileCols is given in
Table A-1 of [HEVC] for the highest level.
max-fps:
The value of max-fps is an integer indicating the maximum
picture rate in units of pictures per 100 seconds that can
be effectively processed by the receiver. The max-fps
parameter MAY be used to signal that the receiver has a
constraint in that it is not capable of processing video
effectively at the full picture rate that is implied by the
highest level and, when present, one or more of the
parameters max-lsr, max-lps, and max-br.
The value of max-fps is not necessarily the picture rate at
which the maximum picture size can be sent, it constitutes
a constraint on maximum picture rate for all resolutions.
Informative note: The max-fps parameter is semantically
different from max-lsr, max-lps, max-cpb, max-dpb, max-
br, max-tr, and max-tc in that max-fps is used to signal
a constraint, lowering the maximum picture rate from
what is implied by other parameters.
The encoder MUST use a picture rate equal to or less than
this value. In cases where the max-fps parameter is absent
the encoder is free to choose any picture rate according to
the highest level and any signaled optional parameters.
The value of max-fps MUST be smaller than or equal to the
full picture rate that is implied by the highest level and,
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when present, one or more of the parameters max-lsr, max-
lps, and max-br.
sprop-max-don-diff:
If tx-mode is equal to "SRST" and there is no NAL unit
naluA that is followed in transmission order by any NAL
unit preceding naluA in decoding order (i.e. the
transmission order of the NAL units is the same as the
decoding order), the value of this parameter MUST be equal
to 0.
Otherwise, if tx-mode is equal to "MRST" or "MRMT", the
decoding order of the NAL units of all the RTP streams is
the same as the NAL unit transmission order and the NAL
unit output order, the value of this parameter MUST be
equal to either 0 or 1.
Otherwise, if tx-mode is equal to "MRST" or "MRMT" and the
decoding order of the NAL units of all the RTP streams is
the same as the NAL unit transmission order but not the
same as the NAL unit output order, the value of this
parameter MUST be equal to 1.
Otherwise, this parameter specifies the maximum absolute
difference between the decoding order number (i.e., AbsDon)
values of any two NAL units naluA and naluB, where naluA
follows naluB in decoding order and precedes naluB in
transmission order.
The value of sprop-max-don-diff MUST be an integer in the
range of 0 to 32767, inclusive.
When not present, the value of sprop-max-don-diff is
inferred to be equal to 0.
sprop-depack-buf-nalus:
This parameter specifies the maximum number of NAL units
that precede a NAL unit in transmission order and follow
the NAL unit in decoding order.
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The value of sprop-depack-buf-nalus MUST be an integer in
the range of 0 to 32767, inclusive.
When not present, the value of sprop-depack-buf-nalus is
inferred to be equal to 0.
When sprop-max-don-diff is present and greater than 0, this
parameter MUST be present and the value MUST be greater
than 0.
sprop-depack-buf-bytes:
This parameter signals the required size of the de-
packetization buffer in units of bytes. The value of the
parameter MUST be greater than or equal to the maximum
buffer occupancy (in units of bytes) of the de-
packetization buffer as specified in Section 6.
The value of sprop-depack-buf-bytes MUST be an integer in
the range of 0 to 4294967295, inclusive.
When sprop-max-don-diff is present and greater than 0, this
parameter MUST be present and the value MUST be greater
than 0. When not present, the value of sprop-depack-buf-
bytes is inferred to be equal to 0.
Informative note: The value of sprop-depack-buf-bytes
indicates the required size of the de-packetization
buffer only. When network jitter can occur, an
appropriately sized jitter buffer has to be available as
well.
depack-buf-cap:
This parameter signals the capabilities of a receiver
implementation and indicates the amount of de-packetization
buffer space in units of bytes that the receiver has
available for reconstructing the NAL unit decoding order
from NAL units carried in one or more RTP streams. A
receiver is able to handle any RTP stream, and all RTP
streams the RTP stream depends on, when present, for which
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the value of the sprop-depack-buf-bytes parameter is
smaller than or equal to this parameter.
When not present, the value of depack-buf-cap is inferred
to be equal to 4294967295. The value of depack-buf-cap
MUST be an integer in the range of 1 to 4294967295,
inclusive.
Informative note: depack-buf-cap indicates the maximum
possible size of the de-packetization buffer of the
receiver only, without allowing for network jitter.
sprop-segmentation-id:
This parameter MAY be used to signal the segmentation tools
present in the bitstream and that can be used for
parallelization. The value of sprop-segmentation-id MUST
be an integer in the range of 0 to 3, inclusive. When not
present, the value of sprop-segmentation-id is inferred to
be equal to 0.
When sprop-segmentation-id is equal to 0, no information
about the segmentation tools is provided. When sprop-
segmentation-id is equal to 1, it indicates that slices are
present in the bitstream. When sprop-segmentation-id is
equal to 2, it indicates that tiles are present in the
bitstream. When sprop-segmentation-id is equal to 3, it
indicates that WPP is used in the bitstream.
sprop-spatial-segmentation-idc:
A base16 [RFC4648] representation of the syntax element
min_spatial_segmentation_idc as specified in [HEVC]. This
parameter MAY be used to describe parallelization
capabilities of the bitstream.
dec-parallel-cap:
This parameter MAY be used to indicate the decoder's
additional decoding capabilities given the presence of
tools enabling parallel decoding, such as slices, tiles,
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and WPP, in the bitstream. The decoding capability of the
decoder may vary with the setting of the parallel decoding
tools present in the bitstream, e.g. the size of the tiles
that are present in a bitstream. Therefore, multiple
capability points may be provided, each indicating the
minimum required decoding capability that is associated
with a parallelism requirement, which is a requirement on
the bitstream that enables parallel decoding.
Each capability point is defined as a combination of 1) a
parallelism requirement, 2) a profile (determined by
profile-space and profile-id), 3) a highest level, and 4) a
maximum processing rate, a maximum picture size, and a
maximum video bitrate that may be equal to or greater than
that determined by the highest level. The parameter's
syntax in ABNF [RFC5234] is as follows:
dec-parallel-cap = "dec-parallel-cap={" cap-point *(","
cap-point) "}"
cap-point = ("w" / "t") ":" spatial-seg-idc 1*(";"
cap-parameter)
spatial-seg-idc = 1*4DIGIT ; (1-4095)
cap-parameter = tier-flag / level-id / max-lsr
/ max-lps / max-br
tier-flag = "tier-flag" EQ ("0" / "1")
level-id = "level-id" EQ 1*3DIGIT ; (0-255)
max-lsr = "max-lsr" EQ 1*20DIGIT ; (0-
18,446,744,073,709,551,615)
max-lps = "max-lps" EQ 1*10DIGIT ; (0-4,294,967,295)
max-br = "max-br" EQ 1*20DIGIT ; (0-
18,446,744,073,709,551,615)
EQ = "="
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The set of capability points expressed by the dec-parallel-
cap parameter is enclosed in a pair of curly braces ("{}").
Each set of two consecutive capability points is separated
by a comma (','). Within each capability point, each set
of two consecutive parameters, and when present, their
values, is separated by a semicolon (';').
The profile of all capability points is determined by
profile-space and profile-id that are outside the dec-
parallel-cap parameter.
Each capability point starts with an indication of the
parallelism requirement, which consists of a parallel tool
type, which may be equal to 'w' or 't', and a decimal value
of the spatial-seg-idc parameter. When the type is 'w',
the capability point is valid only for H.265 bitstreams
with WPP in use, i.e. entropy_coding_sync_enabled_flag
equal to 1. When the type is 't', the capability point is
valid only for H.265 bitstreams with WPP not in use (i.e.
entropy_coding_sync_enabled_flag equal to 0). The
capability-point is valid only for H.265 bitstreams with
min_spatial_segmentation_idc equal to or greater than
spatial-seg-idc.
After the parallelism requirement indication, each
capability point continues with one or more pairs of
parameter and value in any order for any of the following
parameters:
o tier-flag
o level-id
o max-lsr
o max-lps
o max-br
At most one occurrence of each of the above five parameters
is allowed within each capability point.
The values of dec-parallel-cap.tier-flag and dec-parallel-
cap.level-id for a capability point indicate the highest
level of the capability point. The values of dec-parallel-
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cap.max-lsr, dec-parallel-cap.max-lps, and dec-parallel-
cap.max-br for a capability point indicate the maximum
processing rate in units of luma samples per second, the
maximum picture size in units of luma samples, and the
maximum video bitrate (in units of CpbBrVclFactor bits per
second for the VCL HRD parameters and in units of
CpbBrNalFactor bits per second for the NAL HRD parameters
where CpbBrVclFactor and CpbBrNalFactor are defined in
Section A.4 of [HEVC]).
When not present, the value of dec-parallel-cap.tier-flag
is inferred to be equal to the value of tier-flag outside
the dec-parallel-cap parameter. When not present, the
value of dec-parallel-cap.level-id is inferred to be equal
to the value of max-recv-level-id outside the dec-parallel-
cap parameter. When not present, the value of dec-
parallel-cap.max-lsr, dec-parallel-cap.max-lps, or dec-
parallel-cap.max-br is inferred to be equal to the value of
max-lsr, max-lps, or max-br, respectively, outside the dec-
parallel-cap parameter.
The general decoding capability, expressed by the set of
parameters outside of dec-parallel-cap, is defined as the
capability point that is determined by the following
combination of parameters: 1) the parallelism requirement
corresponding to the value of sprop-segmentation-id equal
to 0 for a bitstream, 2) the profile determined by profile-
space, profile-id, profile-compatibility-indicator, and
interop-constraints, 3) the tier and the highest level
determined by tier-flag and max-recv-level-id, and 4) the
maximum processing rate, the maximum picture size, and the
maximum video bitrate determined by the highest level. The
general decoding capability MUST NOT be included as one of
the set of capability points in the dec-parallel-cap
parameter.
For example, the following parameters express the general
decoding capability of 720p30 (Level 3.1) plus an
additional decoding capability of 1080p30 (Level 4) given
that the spatially largest tile or slice used in the
bitstream is equal to or less than 1/3 of the picture size:
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a=fmtp:98 level-id=93;dec-parallel-cap={t:8;level-
id=120}
For another example, the following parameters express an
additional decoding capability of 1080p30, using dec-
parallel-cap.max-lsr and dec-parallel-cap.max-lps, given
that WPP is used in the bitstream:
a=fmtp:98 level-id=93;dec-parallel-cap={w:8;
max-lsr=62668800;max-lps=2088960}
Informative note: When min_spatial_segmentation_idc is
present in a bitstream and WPP is not used, [HEVC]
specifies that there is no slice or no tile in the
bitstream containing more than 4 * PicSizeInSamplesY /
( min_spatial_segmentation_idc + 4 ) luma samples.
include-dph:
This parameter is used to indicate the capability and
preference to utilize or include decoded picture hash (DPH)
SEI messages (See Section D.3.19 of [HEVC]) in the
bitstream. DPH SEI messages can be used to detect picture
corruption so the receiver can request picture repair, see
Section 8. The value is a comma separated list of hash
types that is supported or requested to be used, each hash
type provided as an unsigned integer value (0-255), with
the hash types listed from most preferred to the least
preferred. Example: "include-dph=0,2", which indicates the
capability for MD5 (most preferred) and Checksum (less
preferred). If the parameter is not included or the value
contains no hash types, then no capability to utilize DPH
SEI messages is assumed. Note that DPH SEI messages MAY
still be included in the bitstream even when there is no
declaration of capability to use them, as in general SEI
messages do not affect the normative decoding process and
decoders are allowed to ignore SEI messages.
Encoding considerations:
This type is only defined for transfer via RTP (RFC 3550).
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Security considerations:
See Section 9 of RFC XXXX.
Public specification:
Please refer to Section 13 of RFC XXXX.
Additional information: None
File extensions: none
Macintosh file type code: none
Object identifier or OID: none
Person & email address to contact for further information:
Ye-Kui Wang (yekuiw@qti.qualcomm.com).
Intended usage: COMMON
Author: See Section 14 of RFC XXXX.
Change controller:
IETF Audio/Video Transport Payloads working group delegated
from the IESG.
7.2 SDP Parameters
The receiver MUST ignore any parameter unspecified in this memo.
7.2.1 Mapping of Payload Type Parameters to SDP
The media type video/H265 string is mapped to fields in the
Session Description Protocol (SDP) [RFC4566] as follows:
o The media name in the "m=" line of SDP MUST be video.
o The encoding name in the "a=rtpmap" line of SDP MUST be H265
(the media subtype).
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o The clock rate in the "a=rtpmap" line MUST be 90000.
o The OPTIONAL parameters "profile-space", "profile-id", "tier-
flag", "level-id", "interop-constraints", "profile-
compatibility-indicator", "sprop-sub-layer-id", "recv-sub-
layer-id", "max-recv-level-id", "tx-mode", "max-lsr", "max-
lps", "max-cpb", "max-dpb", "max-br", "max-tr", "max-tc",
"max-fps", "sprop-max-don-diff", "sprop-depack-buf-nalus",
"sprop-depack-buf-bytes", "depack-buf-cap", "sprop-
segmentation-id", "sprop-spatial-segmentation-idc", "dec-
parallel-cap", and "include-dph", when present, MUST be
included in the "a=fmtp" line of SDP. This parameter is
expressed as a media type string, in the form of a semicolon
separated list of parameter=value pairs.
o The OPTIONAL parameters "sprop-vps", "sprop-sps", and "sprop-
pps", when present, MUST be included in the "a=fmtp" line of
SDP or conveyed using the "fmtp" source attribute as specified
in Section 6.3 of [RFC5576]. For a particular media format
(i.e. RTP payload type), "sprop-vps" "sprop-sps", or "sprop-
pps" MUST NOT be both included in the "a=fmtp" line of SDP and
conveyed using the "fmtp" source attribute. When included in
the "a=fmtp" line of SDP, these parameters are expressed as a
media type string, in the form of a semicolon separated list
of parameter=value pairs. When conveyed in the "a=fmtp" line
of SDP for a particular payload type, the parameters "sprop-
vps", "sprop-sps", and "sprop-pps" MUST be applied to each
SSRC with the payload type. When conveyed using the "fmtp"
source attribute, these parameters are only associated with
the given source and payload type as parts of the "fmtp"
source attribute.
Informative note: Conveyance of "sprop-vps", "sprop-sps",
and "sprop-pps" using the "fmtp" source attribute allows
for out-of-band transport of parameter sets in topologies
like Topo-Video-switch-MCU as specified in [RFC5117].
An example of media representation in SDP is as follows:
m=video 49170 RTP/AVP 98
a=rtpmap:98 H265/90000
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a=fmtp:98 profile-id=1;
sprop-vps=<video parameter sets data>
7.2.2 Usage with SDP Offer/Answer Model
When HEVC is offered over RTP using SDP in an Offer/Answer model
[RFC3264] for negotiation for unicast usage, the following
limitations and rules apply:
o The parameters identifying a media format configuration for
HEVC are profile-space, profile-id, tier-flag, level-id,
interop-constraints, profile-compatibility-indicator, and tx-
mode. These media configuration parameters, except level-id,
MUST be used symmetrically when the answerer does not include
recv-sub-layer-id in the answer for the media format (payload
type) or the included recv-sub-layer-id is equal to sprop-sub-
layer-id in the offer. The answerer MUST
1) maintain all configuration parameters with the values
remaining the same as in the offer for the media format
(payload type), with the exception that the value of
level-id is changeable as long as the highest level
indicated by the answer is not higher than that indicated
by the offer;
2) include in the answer the recv-sub-layer-id parameter,
with a value less than the sprop-sub-layer-id parameter
in the offer, for the media format (payload type), and
maintain all configuration parameters with the values
being the same as signalled in the sprop-vps for the
chosen sub-layer representation, with the exception that
the value of level-id is changeable as long as the
highest level indicated by the answer is not higher than
the level indicated by the sprop-vps in offer for the
chosen sub-layer representation; or
3) remove the media format (payload type) completely (when
one or more of the parameter values are not supported).
Informative note: The above requirement for symmetric use
does not apply for level-id, and does not apply for the
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other bitstream or RTP stream properties and capability
parameters.
o The profile-compatibility-indicator, when offered as sendonly,
describe bitstream properties. The answerer MAY accept an RTP
payload type even if the decoder is not capable of handling
the profile indicated by the profile-space, profile-id, and
interop-constraints parameters, but capable of any of the
profiles indicated by the profile-space, profile-
compatibility-indicator, and interop-constraints. However,
when the profile-compatibility-indicator is used in a recvonly
or sendrecv media description, the bitstream using this RTP
payload type is required to conform to all profiles indicated
by profile-space, profile-compatibility-indicator, and
interop-constraints.
o To simplify handling and matching of these configurations, the
same RTP payload type number used in the offer SHOULD also be
used in the answer, as specified in [RFC3264].
o The same RTP payload type number used in the offer for the
media subtype H265 MUST be used in the answer when the answer
includes recv-sub-layer-id. When the answer does not include
recv-sub-layer-id, the answer MUST NOT contain a payload type
number used in the offer for the media subtype H265 unless the
configuration is exactly the same as in the offer or the
configuration in the answer only differs from that in the
offer with a different value of level-id. The answer MAY
contain the recv-sub-layer-id parameter if an HEVC bitstream
contains multiple operation points (using temporal scalability
and sub-layers) and sprop-vps is included in the offer where
information of sub-layers are present in the first video
parameter set contained in sprop-vps. If the sprop-vps is
provided in an offer, an answerer MAY select a particular
operation point indicated in the first video parameter set
contained in sprop-vps. When the answer includes recv-sub-
layer-id that is less than sprop-sub-layer-id in the offer,
all video parameter sets contained in the sprop-vps parameter
in the SDP answer and all video parameter sets sent in-band
for either the offerer-to-answerer direction or the answerer-
to-offerer direction MUST be consistent with the first video
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parameter set in the sprop-vps parameter of the offer (see the
semantics of sprop-vps in Section 7.1 of this document on one
video parameter set being consistent with another video
parameter set), and the bitstream sent in either direction
MUST conform to the profile, tier, level, and constraints of
the chosen sub-layer representation as indicated by the first
profile_tier_level( ) syntax structure in the first video
parameter set in the sprop-vps parameter of the offer.
Informative note: When an offerer receives an answer that
does not include recv-sub-layer-id, it has to compare
payload types not declared in the offer based on the media
type (i.e. video/H265) and the above media configuration
parameters with any payload types it has already declared.
This will enable it to determine whether the configuration
in question is new or if it is equivalent to configuration
already offered, since a different payload type number may
be used in the answer. The ability to perform operation
point selection enables a receiver to utilize the temporal
scalable nature of an HEVC bitstream.
o The parameters sprop-max-don-diff, sprop-depack-buf-nalus, and
sprop-depack-buf-bytes describe the properties of an RTP
stream, and all RTP streams the RTP stream depends on, when
present, that the offerer or the answerer is sending for the
media format configuration. This differs from the normal
usage of the Offer/Answer parameters: normally such parameters
declare the properties of the bitstream or RTP stream that the
offerer or the answerer is able to receive. When dealing with
HEVC, the offerer assumes that the answerer will be able to
receive media encoded using the configuration being offered.
Informative note: The above parameters apply for any RTP
stream and all RTP streams the RTP stream depends on, when
present, sent by a declaring entity with the same
configuration. In other words, the applicability of the
above parameters to RTP streams depends on the source
endpoint. Rather than being bound to the payload type,
the values may have to be applied to another payload type
when being sent, as they apply for the configuration.
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o The capability parameters max-lsr, max-lps, max-cpb, max-dpb,
max-br, max-tr, and max-tc MAY be used to declare further
capabilities of the offerer or answerer for receiving. These
parameters MUST NOT be present when the direction attribute is
"sendonly".
o The capability parameter max-fps MAY be used to declare lower
capabilities of the offerer or answerer for receiving. The
parameters MUST NOT be present when the direction attribute is
"sendonly".
o The capability parameter dec-parallel-cap MAY be used to
declare additional decoding capabilities of the offerer or
answerer for receiving. Upon receiving such a declaration of
a receiver, a sender MAY send a bitstream to the receiver
utilizing those capabilities under the assumption that the
bitstream fulfills the parallelism requirement. A bitstream
that is sent based on choosing a capability point with
parallel tool type 'w' from dec-parallel-cap MUST have
entropy_coding_sync_enabled_flag equal to 1 and
min_spatial_segmentation_idc equal to or larger than dec-
parallel-cap.spatial-seg-idc of the capability point. A
bitstream that is sent based on choosing a capability point
with parallel tool type 't' from dec-parallel-cap MUST have
entropy_coding_sync_enabled_flag equal to 0 and
min_spatial_segmentation_idc equal to or larger than dec-
parallel-cap.spatial-seg-idc of the capability point.
o An offerer has to include the size of the de-packetization
buffer, sprop-depack-buf-bytes, as well as sprop-max-don-diff
and sprop-depack-buf-nalus, in the offer for an interleaved
HEVC bitstream or for the MRST or MRMT transmission mode when
sprop-max-don-diff is greater than 0 for at least one of the
RTP streams. To enable the offerer and answerer to inform
each other about their capabilities for de-packetization
buffering in receiving RTP streams, both parties are
RECOMMENDED to include depack-buf-cap. For interleaved RTP
streams or in MRST or MRMT, it is also RECOMMENDED to consider
offering multiple payload types with different buffering
requirements when the capabilities of the receiver are
unknown.
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o The capability parameter include-dph MAY be used to declare
the capability to utilize decoded picture hash SEI messages
and which types of hashes in any HEVC RTP streams received by
the offerer or answerer.
o The sprop-vps, sprop-sps, or sprop-pps, when present (included
in the "a=fmtp" line of SDP or conveyed using the "fmtp"
source attribute as specified in Section 6.3 of [RFC5576]),
are used for out-of-band transport of the parameter sets (VPS,
SPS, or PPS respectively).
o The answerer MAY use either out-of-band or in-band transport
of parameter sets for the bitstream it is sending, regardless
of whether out-of-band parameter sets transport has been used
in the offerer-to-answerer direction. Parameter sets included
in an answer are independent of those parameter sets included
in the offer, as they are used for decoding two different
bitstreams, one from the answerer to the offerer and the other
in the opposite direction. In case some RTP stream(s) are
sent before SDP offer/answer settles down, in-band parameter
sets MUST be used for those RTP stream parts sent before the
SDP offer/answer.
o The following rules apply to transport of parameter set in the
offerer-to-answerer direction.
o An offer MAY include sprop-vps, sprop-sps, and/or sprop-
pps. If none of these parameters is present in the offer,
then only in-band transport of parameter sets is used.
o If the level to use in the offerer-to-answerer direction
is equal to the default level in the offer, the answerer
MUST be prepared to use the parameter sets included in
sprop-vps, sprop-sps, and sprop-pps (either included in
the "a=fmtp" line of SDP or conveyed using the "fmtp"
source attribute) for decoding the incoming bitstream,
e.g. by passing these parameter set NAL units to the video
decoder before passing any NAL units carried in the RTP
streams. Otherwise, the answerer MUST ignore sprop-vps,
sprop-sps, and sprop-pps (either included in the "a=fmtp"
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line of SDP or conveyed using the "fmtp" source attribute)
and the offerer MUST transmit parameter sets in-band.
o In MRST or MRMT, the answerer MUST be prepared to use the
parameter sets out-of-band transmitted for the RTP stream
and all RTP streams the RTP stream depends on, when
present, for decoding the incoming bitstream, e.g. by
passing these parameter set NAL units to the video decoder
before passing any NAL units carried in the RTP streams.
o The following rules apply to transport of parameter set in the
answerer-to-offerer direction.
o An answer MAY include sprop-vps, sprop-sps, and/or sprop-
pps. If none of these parameters is present in the
answer, then only in-band transport of parameter sets is
used.
o The offerer MUST be prepared to use the parameter sets
included in sprop-vps, sprop-sps, and sprop-pps (either
included in the "a=fmtp" line of SDP or conveyed using the
"fmtp" source attribute) for decoding the incoming
bitstream, e.g. by passing these parameter set NAL units
to the video decoder before passing any NAL units carried
in the RTP streams.
o In MRST or MRMT, the offerer MUST be prepared to use the
parameter sets out-of-band transmitted for the RTP stream
and all RTP streams the RTP stream depends on, when
present, for decoding the incoming bitstream, e.g. by
passing these parameter set NAL units to the video decoder
before passing any NAL units carried in the RTP streams.
o When sprop-vps, sprop-sps, and/or sprop-pps are conveyed using
the "fmtp" source attribute as specified in Section 6.3 of
[RFC5576], the receiver of the parameters MUST store the
parameter sets included in sprop-vps, sprop-sps, and/or sprop-
pps and associate them with the source given as part of the
"fmtp" source attribute. Parameter sets associated with one
source (given as part of the "fmtp" source attribute) MUST
only be used to decode NAL units conveyed in RTP packets from
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the same source (given as part of the "fmtp" source
attribute). When this mechanism is in use, SSRC collision
detection and resolution MUST be performed as specified in
[RFC5576].
For bitstreams being delivered over multicast, the following
rules apply:
o The media format configuration is identified by profile-space,
profile-id, tier-flag, level-id, interop-constraints, profile-
compatibility-indicator, and tx-mode. These media format
configuration parameters, including level-id, MUST be used
symmetrically; that is, the answerer MUST either maintain all
configuration parameters or remove the media format (payload
type) completely. Note that this implies that the level-id
for Offer/Answer in multicast is not changeable.
o To simplify the handling and matching of these configurations,
the same RTP payload type number used in the offer SHOULD also
be used in the answer, as specified in [RFC3264]. An answer
MUST NOT contain a payload type number used in the offer
unless the configuration is the same as in the offer.
o Parameter sets received MUST be associated with the
originating source and MUST only be used in decoding the
incoming bitstream from the same source.
o The rules for other parameters are the same as above for
unicast as long as the three above rules are obeyed.
Table 1 lists the interpretation of all the parameters that MUST
be used for the various combinations of offer, answer, and
direction attributes. Note that the two columns wherein the
recv-sub-layer-id parameter is used only apply to answers,
whereas the other columns apply to both offers and answers.
Table 1. Interpretation of parameters for various combinations
of offers, answers, direction attributes, with and without recv-
sub-layer-id. Columns that do not indicate offer or answer apply
to both.
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sendonly --+
answer: recvonly, recv-sub-layer-id --+ |
recvonly w/o recv-sub-layer-id --+ | |
answer: sendrecv, recv-sub-layer-id --+ | | |
sendrecv w/o recv-sub-layer-id --+ | | | |
| | | | |
profile-space C D C D P
profile-id C D C D P
tier-flag C D C D P
level-id D D D D P
interop-constraints C D C D P
profile-compatibility-indicator C D C D P
tx-mode C C C C P
max-recv-level-id R R R R -
sprop-max-don-diff P P - - P
sprop-depack-buf-nalus P P - - P
sprop-depack-buf-bytes P P - - P
depack-buf-cap R R R R -
sprop-segmentation-id P P P P P
sprop-spatial-segmentation-idc P P P P P
max-br R R R R -
max-cpb R R R R -
max-dpb R R R R -
max-lsr R R R R -
max-lps R R R R -
max-tr R R R R -
max-tc R R R R -
max-fps R R R R -
sprop-vps P P - - P
sprop-sps P P - - P
sprop-pps P P - - P
sprop-sub-layer-id P P - - P
recv-sub-layer-id X O X O -
dec-parallel-cap R R R R -
include-dph R R R R -
Legend:
C: configuration for sending and receiving bitstreams
D: changable configuration, same as C except possible
to answer with a different but consistent value (see the
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semantics of the six parameters related to profile, tier,
and level on these parameters being consistent)
P: properties of the bitstream to be sent
R: receiver capabilities
O: operation point selection
X: MUST NOT be present
-: not usable, when present MUST be ignored
Parameters used for declaring receiver capabilities are in
general downgradable; i.e. they express the upper limit for a
sender's possible behavior. Thus, a sender MAY select to set its
encoder using only lower/lesser or equal values of these
parameters.
When the answer does not include recv-sub-layer-id that is less
than the sprop-sub-layer-id in the offer, parameters declaring a
configuration point are not changeable, with the exception of the
level-id parameter for unicast usage, and these parameters
express values a receiver expects to be used and MUST be used
verbatim in the answer as in the offer.
When a sender's capabilities are declared with the configuration
parameters, these parameters express a configuration that is
acceptable for the sender to receive bitstreams. In order to
achieve high interoperability levels, it is often advisable to
offer multiple alternative configurations. It is impossible to
offer multiple configurations in a single payload type. Thus,
when multiple configuration offers are made, each offer requires
its own RTP payload type associated with the offer. However, it
is possible to offer multiple operation points using one
configuration in a single payload type by including sprop-vps in
the offer and recv-sub-layer-id in the answer.
A receiver SHOULD understand all media type parameters, even if
it only supports a subset of the payload format's functionality.
This ensures that a receiver is capable of understanding when an
offer to receive media can be downgraded to what is supported by
the receiver of the offer.
An answerer MAY extend the offer with additional media format
configurations. However, to enable their usage, in most cases a
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second offer is required from the offerer to provide the
bitstream property parameters that the media sender will use.
This also has the effect that the offerer has to be able to
receive this media format configuration, not only to send it.
7.2.3 Usage in Declarative Session Descriptions
When HEVC over RTP is offered with SDP in a declarative style, as
in Real Time Streaming Protocol (RTSP) [RFC2326] or Session
Announcement Protocol (SAP) [RFC2974], the following
considerations are necessary.
o All parameters capable of indicating both bitstream properties
and receiver capabilities are used to indicate only bitstream
properties. For example, in this case, the parameter profile-
tier-level-id declares the values used by the bitstream, not
the capabilities for receiving bitstreams. This results in
that the following interpretation of the parameters MUST be
used:
o Declaring actual configuration or bitstream properties:
- profile-space
- profile-id
- tier-flag
- level-id
- interop-constraints
- profile-compatibility-indicator
- tx-mode
- sprop-vps
- sprop-sps
- sprop-pps
- sprop-max-don-diff
- sprop-depack-buf-nalus
- sprop-depack-buf-bytes
- sprop-segmentation-id
- sprop-spatial-segmentation-idc
o Not usable (when present, they MUST be ignored):
- max-lps
- max-lsr
- max-cpb
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- max-dpb
- max-br
- max-tr
- max-tc
- max-fps
- max-recv-level-id
- depack-buf-cap
- sprop-sub-layer-id
- dec-parallel-cap
- include-dph
o A receiver of the SDP is required to support all parameters
and values of the parameters provided; otherwise, the receiver
MUST reject (RTSP) or not participate in (SAP) the session.
It falls on the creator of the session to use values that are
expected to be supported by the receiving application.
7.2.4 Parameter Sets Considerations
When out-of-band transport of parameter sets is used, parameter
sets MAY still be additionally transported in-band unless
explicitly disallowed by an application, and some of these
additionally in-band transported parameter sets may update some
of the out-of-band transported parameter sets. Update of a
parameter set refers to sending of a parameter set of the same
type using the same parameter set ID but with different values
for at least one other parameter of the parameter set.
7.2.5 Dependency Signaling in Multi-Stream Mode
If MRST or MRMT is used, the rules on signaling media decoding
dependency in SDP as defined in [RFC5583] apply. The rules on
"hierarchical or layered encoding" with multicast in Section 5.7
of [RFC4566] do not apply. This means that the notation for
Connection Data "c=" SHALL NOT be used with more than one
address, i.e. the sub-field <number of addresses> in the sub-
field <connection-address> of the "c=" field, described in
[RFC4566], must not be present. The order of session dependency
is given from the RTP stream containing the lowest temporal sub-
layer to the RTP stream containing the highest temporal sub-
layer.
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8 Use with Feedback Messages
The following subsections define the use of the Picture Loss
Indication (PLI), Slice Lost Indication (SLI), Reference Picture
Selection Indication (RPSI), and Full Intra Request (FIR)
feedback messages with HEVC. The PLI, SLI, and RPSI messages are
defined in RFC 4585 [RFC4585], and the FIR message is defined in
RFC 5104 [RFC5104].
8.1 Picture Loss Indication (PLI)
As specified in RFC 4585 Section 6.3.1, the reception of a
picture loss indication by a media sender indicates "the loss of
an undefined amount of coded video data belonging to one or more
pictures." Without having any specific knowledge of the setup of
the bitstream (such as: use and location of in-band parameter
sets, non-IDR decoder refresh points, picture structures, and so
forth) a reaction to the reception of an PLI by an HEVC sender
SHOULD be to send an IDR picture and relevant parameter sets;
potentially with sufficient redundancy so to ensure correct
reception. However, sometimes information about the bitstream
structure is known. For example, state could have been
established outside of the mechanisms defined in this document
that parameter sets are conveyed out of band only, and stay
static for the duration of the session. In that case, it is
obviously unnecessary to send them in-band as a result of the
reception of a PLI. Other examples could be devised based on a
priori knowledge of different aspects of the bitstream structure.
In all cases, the timing and congestion control mechanisms of RFC
4585 MUST be observed.
8.2 Slice Loss Indication (SLI)
RFC 4585's Slice Loss Indication can be used to indicate, to a
sender, the loss of a number of Coded Tree Blocks (CTBs) in CTB
raster scan order of a picture. In the SLI's Feedback Control
Indication (FCI) field, the subfield "First" MUST be set to the
CTB address of the first lost CTB. Note that the CTB address is
in CTB raster scan order of a picture. For the first CTB of a
slice segment, the CTB address is the value of
slice_segment_address when present; or 0 when the value of
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first_slice_segement_in_pic_flag is equal to 1; both syntax
elements are in the slice segment header. The subfield "Number"
MUST be set to the number of consecutive lost CTBs, again in CTB
raster scan order of a picture. Note that due to both the
"First" and "Number" are counted in CTBs in CTB raster scan
order, of a picture, not in tile scan order (which is the
bitstream order of CTBs), multiple SLI messages may be needed to
report the loss of one tile covering multiple CTB rows but less
wide than the picture.
The subfield "PictureID" MUST be set to the 6 least significant
bits of a binary representation of the value of PicOrderCntVal,
as defined in [HEVC], of the picture for which the lost CTBs are
indicated. Note that for IDR pictures the syntax element
slice_pic_order_cnt_lsb is not present, but then the value is
inferred to be equal to 0.
As described in RFC 4585, an encoder in a media sender can use
these information to "clean up" the corrupted picture by sending
intra information, while observing the constraints described in
RFC 4585, for example with respect to congestion control. In
many cases, error tracking is required to identify the corrupted
region in the receiver's state (reference pictures) because of
error import in uncorrupted regions of the picture through motion
compensation. Reference picture selection can also be used to
"clean up" the corrupted picture, which is usually more efficient
and less likely to generate congestion than sending intra
information.
In contrast to the video codecs contemplated in RFC 4585 and RFC
5104 [RFC5104], in HEVC, the "macroblock size" is not fixed to
16x16 luma samples, but variable. That, however, does not create
a conceptual difficulty with SLI, because the setting of the CTB
size is a sequence-level functionality, and using a slice loss
indication across CVS boundaries is meaningless as there is no
prediction across sequence boundaries. However, a proper use of
SLI messages is not as straightforward as it was with older,
fixed-macroblock-sized video codecs, as the state of the sequence
parameter set (where the CTB size is located) has to be taken
into account when interpreting the "First" subfield in the FCI.
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8.3 Reference Picture Selection Indication (RPSI)
Feedback based reference picture selection has been shown as a
powerful tool to stop temporal error propagation for improved
error resilience [Girod99][Wang05]. In one approach, the decoder
side tracks errors in the decoded pictures and informs to the
encoder side that a particular picture that has been decoded
relatively earlier is correct and still present in the decoded
picture buffer and requests the encoder to use that correct
picture availability information when encoding the next picture,
so to stop further temporal error propagation. For this
approach, the decoder side should use the RPSI feedback message.
Encoders can encode some long-term reference pictures as
specified in H.264 or HEVC for purposes described in the previous
paragraph without the need of a huge decoded picture buffer. As
shown in [Wang05], with a flexible reference picture management
scheme as in H.264 and HEVC, even a decoded picture buffer size
of two picture storage buffers would work for the approach
described in the previous paragraph.
The field "Native RPSI bit string defined per codec" is a base16
[RFC4648] representation of the 8 bits consisting of 2 most
significant bits equal to 0 and 6 bits of nuh_layer_id, as
defined in [HEVC], followed by the 32 bits representing the value
of the PicOrderCntVal (in network byte order), as defined in
[HEVC], for the picture that is indicated by the RPSI feedback
message.
The use of the RPSI feedback message as positive acknowledgement
with HEVC is deprecated. In other words, the RPSI feedback
message MUST only be used as a reference picture selection
request, such that it can also be used in multicast.
8.4 Full Intra Request (FIR)
The purpose of the FIR message is to force an encoder to send an
independent decoder refresh point as soon as possible (observing,
for example, the congestion control related constraints set out
in RFC 5104).
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Upon reception of a FIR, a sender MUST send an IDR picture.
Parameter sets MUST also be sent, except when there is a priori
knowledge that the parameter sets have been correctly
established. A typical example for that is an understanding
between sender and receiver, established by means outside this
document, that parameter sets are exclusively sent out of band.
9 Security Considerations
The scope of this Security Considerations section is limited to
the payload format itself, and to one feature of HEVC that may
pose a particularly serious security risk if implemented naively.
The payload format, in isolation, does not form a complete
system. Implementers are advised to read and understand relevant
security related documents, especially those pertaining to RTP
(see the security considerations section in RFC 3550 [RFC3550]),
and the security of the call control stack chosen (that may make
use of the media type registration of this memo). Implementers
should also consider known security vulnerabilities of video
coding and decoding implementations in general and avoid those.
Within this RTP payload format, and with the exception of the
user data SEI message as described below, no security threats
other than those common to RTP payload formats are known. In
other words, neither the various media plane based mechanisms,
nor the signaling part of this memo, seems to pose a security
risk beyond those common to all RTP based systems.
RTP packets using the payload format defined in this
specification are subject to the security considerations
discussed in the RTP specification [RFC3550], and in any
applicable RTP profile such as RTP/AVP [RFC3551], RTP/AVPF
[RFC4585], RTP/SAVP [RFC3711], or RTP/SAVPF [RFC5124]. However,
as "Securing the RTP Protocol Framework: Why RTP Does Not Mandate
a Single Media Security Solution" RFC 7202 [RFC7202] discusses,
it is not an RTP payload format's responsibility to discuss or
mandate what solutions are used to meet the basic security goals
like confidentiality, integrity and source authenticity for RTP
in general. This responsibility lays on anyone using RTP in an
application. They can find guidance on available security
mechanisms and important considerations in Options for Securing
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RTP Sessions [RFC7201]. Applications SHOULD use one or more
appropriate strong security mechanisms. The rest of this
security consideration section discusses the security impacting
properties of the payload format itself.
Because the data compression used with this payload format is
applied end-to-end, any encryption needs to be performed after
compression. A potential denial-of-service threat exists for
data encodings using compression techniques that have non-uniform
receiver-end computational load. The attacker can inject
pathological datagrams into the bitstream that are complex to
decode and that cause the receiver to be overloaded. H.265 is
particularly vulnerable to such attacks, as it is extremely
simple to generate datagrams containing NAL units that affect the
decoding process of many future NAL units. Therefore, the usage
of data origin authentication and data integrity protection of at
least the RTP packet is RECOMMENDED, for example, with SRTP
[RFC3711].
Like [H.264], HEVC includes a user data Supplementary Enhancement
Information (SEI) message. This SEI message allows inclusion of
an arbitrary bitstring into the video bitstream. Such a bitstring
could include JavaScript, machine code, and other active content.
HEVC leaves the handling of this SEI message to the receiving
system. In order to avoid harmful side effects of the user data
SEI message, decoder implementations cannot naviely trust its
content. For example, it would be a bad and insecure
implementation practice to forward any JavaScript a decoder
implementation detects to a web browser. The safest way to deal
with user data SEI messages is to simply discard them, but that
can have negative side effects on the quality of experience by
the user.
End-to-end security with authentication, integrity, or
confidentiality protection will prevent a MANE from performing
media-aware operations other than discarding complete packets.
In the case of confidentiality protection, it will even be
prevented from discarding packets in a media-aware way. To be
allowed to perform such operations, a MANE is required to be a
trusted entity that is included in the security context
establishment.
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10 Congestion Control
Congestion control for RTP SHALL be used in accordance with RTP
[RFC3550] and with any applicable RTP profile, e.g. AVP
[RFC3551]. If best-effort service is being used, an additional
requirement is that users of this payload format MUST monitor
packet loss to ensure that the packet loss rate is within an
acceptable range. Packet loss is considered acceptable if a TCP
flow across the same network path, and experiencing the same
network conditions, would achieve an average throughput, measured
on a reasonable timescale, that is not less than all RTP streams
combined is achieving. This condition can be satisfied by
implementing congestion control mechanisms to adapt the
transmission rate, the number of layers subscribed for a layered
multicast session, or by arranging for a receiver to leave the
session if the loss rate is unacceptably high.
The bitrate adaptation necessary for obeying the congestion
control principle is easily achievable when real-time encoding is
used, for example by adequately tuning the quantization
parameter.
However, when pre-encoded content is being transmitted, bandwidth
adaptation requires the pre-coded bitstream to be tailored for
such adaptivity. The key mechanism available in HEVC is temporal
scalability. A media sender can remove NAL units belonging to
higher temporal sub-layers (i.e. those NAL units with a high
value of TID) until the sending bitrate drops to an acceptable
range. HEVC contains mechanisms that allow the lightweight
identification of switching points in temporal enhancement
layers, as discussed in Section 1.1.2 of this memo. An HEVC
media sender can send packets belonging to NAL units of temporal
enhancement layers starting from these switching points to probe
for available bandwidth and to utilized bandwidth that has been
shown to be available.
Above mechanisms generally work within a defined profile and
level and, therefore, no renegotiation of the channel is
required. Only when non-downgradable parameters (such as
profile) are required to be changed does it become necessary to
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terminate and restart the RTP stream(s). This may be
accomplished by using different RTP payload types.
MANEs MAY remove certain unusable packets from the RTP stream
when that RTP stream was damaged due to previous packet losses.
This can help reduce the network load in certain special cases.
For example, MANES can remove those FUs where the leading FUs
belonging to the same NAL unit have been lost or those dependent
slice segments when the leading slice segments belonging to the
same slice have been lost, because the trailing FUs or dependent
slice segments are meaningless to most decoders. MANES can also
remove higher temporal scalable layers if the outbound
transmission (from the MANE's viewpoint) experiences congestion.
11 IANA Consideration
A new media type, as specified in Section 7.1 of this memo,
should be registered with IANA.
12 Acknowledgements
Muhammed Coban and Marta Karczewicz are thanked for discussions
on the specification of the use with feedback messages and other
aspects in this memo. Jonathan Lennox and Jill Boyce are thanked
for their contributions to the PACI design included in this memo.
Rickard Sjoberg, Arild Fuldseth, Bo Burman, Magnus Westerlund,
and Tom Kristensen are thanked for their contributions to
parallel processing related signalling. Magnus Westerlund,
Jonathan Lennox, Bernard Aboba, Jonatan Samuelsson, Roni Even,
Rickard Sjoberg, Sachin Deshpande, Woo Johnman, Mo Zanaty, Ross
Finlayson, Danny Hong, Bo Burman, Ben Campbell, Brian Carpenter,
Qin Wu, and Stephen Farrell made valuable reviewing comments that
led to improvements.
This document was prepared using 2-Word-v2.0.template.dot, and
the .txt file was generated using the online Word-post procesor
available here: http://www.isi.edu/touch/tools/rfc-word-
template.html.
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13 References
13.1 Normative References
[HEVC] ITU-T Recommendation H.265, "High efficiency video
coding", April 2013.
[H.264] ITU-T Recommendation H.264, "Advanced video coding for
generic audiovisual services", April 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer
Model with Session Description Protocol (SDP)", RFC
3264, June 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and
Jacobson, V., "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3551] Schulzrinne, H. and Casner, S., "RTP Profile for Audio
and Video Conferences with Minimal Control", STD 65,
RFC 3551, July 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and
Norrman, K., "The Secure Real-time Transport Protocol
(SRTP)", RFC 3711, March 2004.
[RFC4566] Handley, M., Jacobson, V., and Perkins, C., "SDP:
Session Description Protocol", RFC 4566, July 2006.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and Rey,
J., "Extended RTP Profile for Real-time Transport
Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC
4585, July 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
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[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and Burman,
B., "Codec Control Messages in the RTP Audio-Visual
Profile with Feedback (AVPF)", RFC 5104, February 2008.
[RFC5124] Ott, J. and Carrara, E., "Extended Secure RTP Profile
for Real-time Transport Control Protocol (RTCP)-Based
Feedback (RTP/SAVPF)", RFC 5124, February 2008.
[RFC5234] Crocker, D. and Overell, P., "Augmented BNF for Syntax
Specifications: ABNF", RFC 5234, January 2008.
[RFC5576] Lennox, J., Ott, J., and Schierl, T., "Source-Specific
Media Attributes in the Session Description Protocol",
RFC 5576, June 2009.
[RFC5583] Schierl, T. and Wenger, S., "Signaling Media Decoding
Dependency in the Session Description Protocol (SDP)",
RFC 5583, July 2009.
13.2 Informative References
[3GPDASH] 3GPP TS 26.247, "Transparent end-to-end Packet-switched
Streaming Service (PSS); Progressive Download and
Dynamic Adaptive Streaming over HTTP (3GP-DASH)",
v12.1.0, December 2013.
[3GPPFF] 3GPP TS 26.244, "Transparent end-to-end packet switched
streaming service (PSS); 3GPP file format (3GP)",
v12.20, December 2013.
[CABAC] Sole, J., Joshi, R., Nguyen, N., Ji, T., Karczewicz,
M., Clare, G., Henry, F., and Duenas, A., "Transform
coefficient coding in HEVC", IEEE Transactions on
Circuts and Systems for Video Technology, Vol. 22, No.
12, pp. 1765-1777, December 2012.
[Girod99] Girod, B. and Faerber, F., "Feedback-based error
control for mobile video transmission", Proceedings
IEEE, Vol. 87, No. 10, pp. 1707-1723, October 1999.
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[HEVC draft v2]
Draft version 2 of HEVC, "High Efficiency Video Coding
(HEVC) Range Extensions text specification: Draft 7",
JCT-VC document JCTVC-Q1005, 17th JCT-VC meeting, 27
March - 4 April 2014, Valencia, Spain.
[I-D.ietf-avtcore-rtp-multi-stream]
Lennox, J., Westerlund, M., Wu, W., and C. Perkins,
"Sending Multiple Media Streams in a Single RTP
Session", draft-ietf-avtcore-rtp-multi-stream-09 (work
in progress), September 2015.
[I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings,
"Multiplexing Negotiation Using Session Description
Protocol (SDP) Port Numbers", draft-ietf-mmusic-sdp-
bundle-negotiation-23 (work in progress), July 2015.
[I-D.ietf-avtext-rtp-grouping-taxonomy]
Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G.,
and Burman, B. "A Taxonomy of Grouping Semantics and
Mechanisms for Real-Time Transport", draft-ietf-avtext-
rtp-grouping-taxonomy-08 (work in progress), July 2015.
[ISOBMFF] IS0/IEC 14496-12 | 15444-12: "Information technology -
Coding of audio-visual objects - Part 12: ISO base
media file format" | "Information technology - JPEG
2000 image coding system - Part 12: ISO base media file
format", 2012.
[JCTVC-J0107]
Wang, Y.-K., Chen, Y., Joshi, R., and Ramasubramonian,
K., "AHG9: On RAP pictures", JCT-VC document JCTVC-
L0107, 10th JCT-VC meeting, July 2012, Stockholm,
Sweden.
[MPEG2S] ISO/IEC 13818-1, "Information technology - Generic
coding of moving pictures and associated audio
information: Systems", 2013.
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[MPEGDASH] ISO/IEC 23009-1, "Information technology - Dynamic
adaptive streaming over HTTP (DASH) - Part 1: Media
presentation description and segment formats", 2012.
[RFC2326] Schulzrinne, H., Rao, A., and Lanphier R., "Real Time
Streaming Protocol (RTSP)", RFC 2326, April 1998.
[RFC2974] Handley, M., Perkins C., and Whelan E., "Session
Announcement Protocol", RFC 2974, October 2000.
[RFC5117] Westerlund, M. and Wenger, S., "RTP Topologies", RFC
5117, January 2008.
[RFC6051] Perkins, C. and T. Schierl, "Rapid Synchronisation of
RTP Flows", RFC 6051, November 2010.
[RFC6184] Wang, Y.-K., Even, R., Kristensen, T., and R. Jesup,
"RTP Payload Format for H.264 Video", RFC 6184, May
2011.
[RFC6190] Wenger, S., Wang, Y.-K., Schierl, T., and A.
Eleftheriadis, "RTP Payload Format for Scalable Video
Coding", RFC 6190, May 2011.
[RFC7201] Westerlund, M. and Perkins, C., "Options for Securing
RTP Sessions", RFC 7201, April 2014.
[RFC7202] Perkins, C. and Westerlund, M., "Securing the RTP
Framework: Why RTP Does Not Mandate a Single Media
Security Solution", RFC 7202, April 2014.
[Wang05] Wang, Y.-K., Zhu, C., and Li, H., "Error resilient
video coding using flexible reference fames", Visual
Communications and Image Processing 2005 (VCIP 2005),
July 2005, Beijing, China.
14 Authors' Addresses
Ye-Kui Wang
Qualcomm Incorporated
5775 Morehouse Drive
San Diego, CA 92121, USA
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Phone: +1-858-651-8345
EMail: yekui.wang@gmail.com
Yago Sanchez
Fraunhofer HHI
Einsteinufer 37
D-10587 Berlin, Germany
Phone: +49-30-31002-227
Email: yago.sanchez@hhi.fraunhofer.de
Thomas Schierl
Fraunhofer HHI
Einsteinufer 37
D-10587 Berlin, Germany
Phone: +49-30-31002-227
Email: ts@thomas-schierl.de
Stephan Wenger
Vidyo, Inc.
433 Hackensack Ave., 7th floor
Hackensack, N.J. 07601, USA
Phone: +1-415-713-5473
EMail: stewe@stewe.org
Miska M. Hannuksela
Nokia Corporation
P.O. Box 1000
33721 Tampere, Finland
Phone: +358-7180-08000
EMail: miska.hannuksela@nokia.com
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