Internet DRAFT - draft-ietf-avt-smpte292-video


INTERNET-DRAFT                                              Ladan Gharai
<draft-ietf-avt-smpte292-video-08.txt>                           USC/ISI
                                                           Colin Perkins
                                                            Gary Goncher
                                                          Allison Mankin
                                                        December 2, 2002

                  RTP Payload Format for SMPTE 292M Video

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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This memo specifies a RTP payload format for encapsulating uncompressed
High Definition Television (HDTV) as defined by the Society of Motion
Picture and Television Engineers standard, SMPTE 292M. SMPTE is the main
standardizing body in the motion imaging industry and the SMPTE 292M
standard defines a bit-serial digital interface for local area HDTV

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1.  Introduction

[Note to RFC Editor: All "RFC XXXX" in the IANA considerations section
should be filled in with the RFC number of this memo, when published.]

The serial digital interface, SMPTE 292M[1], defines a universal medium
of interchange for uncompressed High Definition Television (HDTV)
between various types of video equipment (cameras, encoders, VTRs,
etc.). SMPTE 292M stipulates that the source data be in 10 bit words and
the total data rate be either 1.485 Gbps or 1.485/1.001 Gbps.

The use of a dedicated serial interconnect is appropriate in a studio
environment, but it is desirable to leverage the widespread availability
of high bandwidth IP connectivity to allow efficient wide area delivery
of SMPTE 292M format content. Accordingly, this memo defines an RTP
payload format for SMPTE 292M format video.

It is to be noted that SMPTE 292M streams have a constant high bit rate
and are not congestion controlled. Accordingly, use of this payload
format should be tightly controlled and limited to private networks or
those networks that provide resource reservation and enhanced quality of
service. This is discussed further in section 9 "Security

This memo only addresses the transfer of uncompressed HDTV. Compressed
HDTV is a subset of MPEG-2 [9], which is fully described in document
A/53 [10] of the Advanced Television Standards Committee. The ATSC has
also adopted the MPEG-2 transport system (ISO/IEC 13818-1)[11].
Therefore RFC 2250 [12] sufficiently describes transport for compressed
HDTV over RTP.

2.  Overview of SMPTE 292M

A SMPTE 292M television line comprises two interleaved streams, one
containing the luminance (Y) samples, the other chrominance (CrCb)
values. Since chrominance is horizontally sub-sampled (4:2:2 coding) the
lengths of the two streams match (see Figure 3 of SMPTE 292M[1]).  In
addition to being the same length the streams also have identical
structures: each stream is divided into four parts, (figure 1): (1)
start of active video timing reference (SAV); (2) digital active line;
(3) end of active video timing reference (EAV); and (4) digital line
blanking.  A SMPTE 292M line may also carry horizontal ancillary data
(H-ANC) or vertical ancillary data (V-ANC) instead of the blanking
level, and likewise, ancillary data may be transported instead of a
digital active line.

The EAV and SAV are made up of three 10 bit words, with constant values

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of 0x3FF 0x000 0x000  and an additional word (designated as XYZ in
figure 2), carrying a number of flags. This includes an F flag which
designate which field (1 or 2) the line is transporting and also a V
flag which indicates field blanking. Table 1, further displays the code
values in SAV and EAV.  After EAV, are two words LN0 and LN1 (Table 2),
which carry the 11 bit line number for the SMPTE 292M line. The Cyclic
Redundancy Check, CRC, is also a two word value, shown as CR0 and CR1 in
figure 2.

     |            | Digital Line Blanking |     | Digital Active Line |
     | EAV+LN+CRC | (Blanking level or    | SAV |  (Active Picture or |
     |            |  Ancillary Data)      |     |   Ancillary Data)   |

                       Figure 1. The SMPTE 292M line format.

       0       20      40      60     80       0      20      40
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       +-+-+-+-+-+-+-+-+
       |3FF| 0 | 0 |XYZ|LN1|LN2|CR0|CR1|       |3FF| 0 | 0 |XYZ|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       +-+-+-+-+-+-+-+-+
       <---- EAV -----> <- LN-> <- CRC->       <----- SAV ----->

                      Figure 2. Timing reference format.

       |      (MSB)                                        (LSB) |
       | Word    9    8    7    6    5    4    3    2    1    0  |
       | 3FF     1    1    1    1    1    1    1    1    1    1  |
       | 000     0    0    0    0    0    0    0    0    0    0  |
       | 000     0    0    0    0    0    0    0    0    0    0  |
       | XYZ     1    F    V    H    P    P    P    P    P    P  |
       | NOTES:                                                  |
       |     F=0 during field 1; F=1 during field 2.             |
       |     V=0 elsewhere; V=1 during field blanking.           |
       |     H=0 in SAV; H=1 in EAV.                             |
       |     MSB=most significant bit; LSB=least significant bit.|
       |     P= protected bits defined in Table 2 of SMPTE 292M  |
                    Table 1: Timing reference codes.

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       |      (MSB)                                        (LSB) |
       | Word    9    8    7    6    5    4    3    2    1    0  |
       |  LN0    R    L6   L5   L4   L3   L2   L1   L0   R    R  |
       |  LN1    R     R    R    R   L10  L9   L8   L7   R    R  |
       | NOTES:                                                  |
       |    LN0 - L10 - line number in binary code.              |
       |    R = reserved, set to "0".                            |
                    Table 2: Line number data.

The number of words and format for active lines and line blanking is
defined by source format documents. Currently, source video formats
transfered by SMPTE 292M include SMPTE 260M, 295M, 274M and 296M[5-8].
In this memo we specify how to transfer SMPTE 292M over RTP,
irrespective of the source format.

3.  Conventions Used in this Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
document are to be interpreted as described in RFC 2119[2].

4.  Payload Design

Each SMPTE 292M data line is packetized into one or more  RTP packets.
This includes all timing signals, blanking levels, active lines and/or
ancillary data.  Start of active video (SAV) and end of active video
(EAV+LN+CRC) signals MUST NOT be fragmented across packets, as the SMPTE
292M decoder uses them to detect the start of scan lines.

The standard RTP header is followed by a 4 octet payload header. All
information in the payload header pertains to the first data sample in
the packet. The end of a video frame (the packet containing the last
sample before the EAV) is marked by the M bit in the RTP header.

The payload header contains a 16 bit extension to the standard 16 bit
RTP sequence number, thereby extending the sequence number to 32 bits
and enabling RTP to  accommodate HDTV's high data rates. At 1.485 Gbps,
with packet sizes of at least one thousand octets, 32 bits allows for an
approximate 6 hour period before the sequence number wraps around. Given
the same assumptions, the standard 16 bit  RTP sequence number wraps

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around in less than a second (336 milliseconds) which is clearly not
sufficient for the purpose of detecting loss and out of order packets.

A 148.5 MHz (or 148.5/1.001 MHz) time-stamp is used as the RTP
timestamp.  This allows the receiver to reconstruct the timing of the
SMPTE 292M stream, without knowledge of the exact type of source format
(e.g. SMPTE 274M or SMPTE 296M). With this timestamp, the location of
the first byte of each packet can be uniquely identified in the SMPTE
292M stream. At 148.5 MHz the 32 bit timestamp wraps around in 21

The payload header also carries the 11 bit line number from the SMPTE
292M timing signals. This provides more information at the application
level and adds a level of resiliency, in case the packet containing the
EAV is lost.

The bit length of both timing signals, SAV and EAV+LN+CRC, are multiples
of 8 bits, 40 bits and 80 bits, respectively, and therefore are
naturally octet aligned.

For the video content it is desirable for the video to both octet align
when packetized and also adhere to the principles of application level
framing, also known as ALF [13]. For YCrCb video, the ALF principle
translates into not fragmenting related luminance and chrominance values
across packets. For example with the 4:2:0 color subsampling a 4 pixel
group is represented by 6 values, Y1 Y2 Y3 Y4 Cr Cb, and video content
should be packetized such that these values are not fragmented across 2
packets. However, with 10 bit words this is a 60 bit value which is not
octet aligned. To be both octet aligned, and adhere to ALF, an ALF unit
must represent 2 groups of 4 Pixels, thereby becoming octet aligned on a
15 octet boundary. This length is referred to as the pixel group or
pgroup, and it is conveyed in the SDP parameters. Table 3 displays the
pgroup value for various color samplings. Typical source formats use
4:2:2 sampling, and require a pgroup of 5 octets, other values are
included for completeness.

The contents of the Digital Active Line SHOULD NOT be fragmented within
a pgroup. A pgroup of 1 indicates that data may be split at any octet
boundary (this is applicable to instances where the source format is not
known). The SAV and EAV+LN+CRC fields MUST NOT be fragmented.

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             |   Color            10  bit                            |
             |Subsampling  Pixels  words    aligned on octet#  pgroup|
             |   4:2:0   |   4   |  6*10  |   2*60/8 = 15     |  15  |
             |   4:2:2   |   2   |  4*10  |     40/8 = 5      |   5  |
             |   4:4:4   |   1   |  3*10  |   4*30/8 = 15     |  15  |
                       Table 3. Color subsampling and pgroups.

5.  RTP Packetization

The standard RTP header is followed by a 4 octet payload header, and the
payload data, 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
      | V |P|X|   CC  |M|    PT       |     sequence# (low bits)      |
      |                     time stamp                                |
      |                        ssrc                                   |
      |    sequence# (high bits)      |F|V| Z |        line no        |
      |                                                               |
      :                      SMPTE 292M data                          :
      :                                                               :
      |                                                               |
          Figure 4: RTP Packet showing SMPTE 292M headers and payload

5.1.  The RTP Header

The following fields of the RTP fixed header are used for SMPTE 292M
encapsulation (the other fields in the RTP header are used in their
usual manner):

Payload Type (PT): 7 bits
     A dynamically allocated  payload type field which designates the

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     payload as SMPTE 292M.

Timestamp: 32 bits
     For a SMPTE 292M transport stream at 1.485 Gbps (or 1.485/1.001
     Gbps), the timestamp field contains a 148.5 MHz (or 148.5/1.001
     MHz) timestamp, respectively. This allows for a unique timestamp
     for each 10 bit word.

Marker bit (M): 1 bit
     The Marker bit denotes the end of a video frame, and is set to 1
     for the last packet of the video frame and is otherwise  set to 0
     for all other packets.

Sequence Number (low bits): 16 bits
     The low order bits for RTP sequence counter. The standard 16 bit
     RTP  sequence number is augmented with another 16 bits in the
     payload header in order to accommodate the 1.485 Gbps data rate of
     SMPTE 292M.

5.2.  Payload Header

Sequence Number (high bits):  16 bits
     The high order bits for the 32 bit RTP sequence counter, in network
     byte order.

F: 1 bit
     The F bit as defined in the SMPTE 292M timing signals (see
     Table 1). F=1 identifies field 2 and F=0 identifies field 1.

V: 1 bit
     The V  bit as defined in the SMPTE 292M timing signals (see
     Table 1).  V=1 during field blanking, and V=0 else where.

Z: 2 bits
     SHOULD be set to zero by the sender and MUST be ignored by

Line No: 11 bits
     The line number of the source data format, extracted from the
     SMPTE 292M stream (see Table 2). The line number MUST correspond
     to the line number of the first 10 bit word in the packet.

6.  RTCP Considerations

RFC1889 recommends transmission of RTCP packets every 5 seconds or at a
reduced minimum in seconds of 360 divided by the session bandwidth in

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kilobits/second. At 1.485 Gbps the reduced minimum interval computes to
0.2ms or 4028 packets per second.

It should be noted that the sender's octet count in SR packets wraps
around in 23 seconds, and that the cumulative  number of packets lost
wraps around in 93 seconds. This means these two fields cannot
accurately represent octet count and number of packets lost since the
beginning of transmission, as defined in RFC1889. Therefore for network
monitoring purposes or any other application which requires the sender's
octet count and the cumulative number of packets lost since the
beginning of transmission, the application itself must keep track of the
number of rollovers of these fields via a counter.

7.  IANA Considerations

This document defines a new RTP payload format and associated MIME type,
SMPTE292M. The MIME registration form for SMPTE 292M video is enclosed

MIME media type name: video

MIME subtype name: SMPTE292M

Required parameters: rate
  The RTP timestamp clock rate. The clock runs at either 148500000 Hz
  or 148500000/1.001 Hz. If the latter rate is used a timestamp of
  148351648 MUST be used, and receivers MUST interpret this as
  148500000/1.001 Hz.

Optional parameters: pgroup
  The RECOMMENDED grouping for aligning 10 bit words and octets.
  Defaults to 1 octet, if not present.

Encoding considerations: SMPTE292M video can be transmitted with
  RTP as specified in RFC XXXX.

Security considerations: see RFC XXXX section 9.

Interoperability considerations: NONE

Published specification: SMPTE292M
                         RFC XXXX

Applications which use this media type:
                         Video communication.

Additional information: None

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Magic number(s): None

File extension(s): None

Macintosh File Type Code(s): None

Person & email address to contact for further information:
   Ladan Gharai <>
   IETF AVT working group.

Intended usage: COMMON

Author/Change controller:
      Ladan Gharai <>

8.  Mapping to SDP Parameters

Parameters are mapped to SDP [14] as follows:

   m=video 30000 RTP/AVP 111
   a=rtpmap:111 SMPTE292M/148500000
   a=fmtp:111  pgroup=5

In this example, a dynamic payload type 111 is used for SMPTE292M. The
RTP timestamp is 148500000 Hz and the SDP parameter pgroup, indicates
that for video data after the SAV signal, must be packetized in
multiples of 5 octets.

9.  Security Considerations

RTP sessions using the payload format defined in this specification are
subject to the security considerations discussed in the RTP
specification [3] and any appropriate RTP profile (e.g. [4]).

This payload format does not exhibit any significant non-uniformity in
the receiver side computational complexity for packet processing to
cause a potential denial-of-service threat for intended receivers.

The bandwidth of this payload format is high enough (1.485 Gbps without
the RTP overhead) to cause potential for denial-of-service if
transmitted onto most currently available Internet paths. Since
congestion control is not possible for SMPTE-292M over RTP flows, use of
the payload SHOULD be narrowly limited to suitably connected network
endpoints, or to networks where QoS guarantees are available.

If QoS enhanced service is used, RTP receivers SHOULD monitor packet

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loss to ensure that the service that was requested is actually being
delivered.  If it is not, then they SHOULD assume that they are
receiving best-effort service and behave accordingly.

If best-effort service is being used, RTP receivers MUST monitor packet
loss to ensure that the packet loss rate is within acceptable parameters
and MUST leave the session is the loss rate is too high. The loss rate
is considered acceptable if a TCP flow across the same network path,
experiencing the same network conditions, would achieve an average
throughput, measured on a reasonable timescale, that is not less than
the RTP flow is achieving. Since congestion control is not possible for
SMPTE-292M flows, this condition can only be satisfied if receivers
leave the session if the loss rate is unacceptably high.

10.  Full Copyright Statement

Copyright (C) The Internet Society (2002). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included
on all such copies and derivative works.

However, this document itself may not be modified in any way, such as by
removing the copyright notice or references to the Internet Society or
other Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be followed,
or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an "AS

11.  Authors' Addresses

 Ladan Gharai

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 Colin Perkins

 Allison Mankin
 USC Information Sciences Institute
 3811 N. Fairfax Drive
 Arlington, VA 22203-1695

 Gary Goncher
 Tektronix, Inc.
 P.O. Box 500, M/S 50-480
 Beaverton, OR  97077

12.  Acknowledgment

We would like to thank David Richardson for his insightful comments and
contributions to the draft. We would also like to thank Chuck Harrison
for his input and for explaining the intricacies of SMPTE 292M.

13.  Normative References

[1] Society of Motion Picture and Television Engineers,
    Bit-Serial Digital Interface for High-Definition Television
    Systems, SMPTE 292M-1998.

[2] S. Bradner, "Key words for use in RFCs to Indicate
    Requirement Levels", RFC 2119.

[3] H. Schulzrinne, S. Casner, R. Frederick and V. Jacobson, "RTP: A
    Transport Protocol for Real-Time Applications", IETF, Work in
    Progress (draft-ietf-avt-rtp-new-11.txt)

[4] H. Schulzrinee and S. Casner, "RTP Profile for Audio and Video
    Conferences with Minimal Control", IETF, Work in progress,

14.  Informative References

[5] Society of Motion Picture and Television Engineers,
    Digital Representation and Bit-Parallel Interface - 1125/60
    High-Definition Production System, SMPTE 260M-1999.

[6] Society of Motion Picture and Television Engineers,

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    1920x1080 50Hz, Scanning and Interface, SMPTE 295M-1997.

[7] Society of Motion Picture and Television Engineers,
    1920x1080 Scanning and Analog and Parallel Digital Interfaces
    for Multiple Picture Rates, SMPTE 274M-1998.

[8] Society of Motion Picture and Television Engineers,
    1280x720 Scanning, Analog and Digital Representation and Analog
    Interfaces, SMPTE 296M-1998.

[9] ISO/IEC International Standard 13818-2; "Generic coding of
    moving pictures and associated audio information: Video", 1996.

[10] ATSC Digital Television Standard Document A/53, September 1995,

[11] ISO/IEC International Standard 13818-1; "Generic coding of
     moving pictures and associated audio information: Systems",1996.

[12] Hoffman, Fernando, Goyal, Civanlar, "RTP Payload Format for
     MPEG1/MPEG2 Video", RFC 2250, IETF, January 1998.

[13] Clark, D. D., and Tennenhouse, D. L., "Architectural Considerations
     for a New Generation of Protocols", In Proceedings of SIGCOMM '90
     (Philadelphia, PA, Sept. 1990), ACM.

[14] M. Handley and V. Jacobson, "SDP: Session Description Protocol",
     RFC 2327, April 1998.

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