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Network Working Group                                          L. GharaiRequest for Comments: 3497                                    C. PerkinsCategory: Standards Track                                        USC/ISI                                                              G. Goncher                                                               Tektronix                                                               A. Mankin                                           Bell Labs, Lucent Corporation                                                              March 2003RTP Payload Format forSociety of Motion Picture and Television Engineers (SMPTE) 292M VideoStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2003).  All Rights Reserved.Abstract   This memo specifies an RTP payload format for encapsulating   uncompressed High Definition Television (HDTV) as defined by the   Society of Motion Picture and Television Engineers (SMPTE) 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 transport.1.  Introduction   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 content.  Accordingly, this memo   defines an RTP payload format for SMPTE 292M format video.Gharai, et al.              Standards Track                     [Page 1]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 2003   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 insection 9.   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].  ThereforeRFC 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; 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 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 designates 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), that 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.Gharai, et al.              Standards Track                     [Page 2]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 2003         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.         +---------------------------------------------------------+         |      (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 the 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.Gharai, et al.              Standards Track                     [Page 3]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 20033.  Conventions Used in this Document   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 inBCP 14,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 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 sample of each packet can be uniquely   identified in the SMPTE 292M stream.  At 148.5 MHz, the 32 bit   timestamp wraps around in 21 seconds.   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.Gharai, et al.              Standards Track                     [Page 4]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 2003   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.         +-------------------------------------------------------+         |   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.Gharai, et al.              Standards Track                     [Page 5]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 20035.  RTP Packetization   The standard RTP header is followed by a 4 octet payload header, and   the payload data, 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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | V |P|X|   CC  |M|    PT       |     sequence# (low bits)      |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                     time stamp                                |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                        ssrc                                   |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |    sequence# (high bits)      |F|V| Z |        line no        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                                                               |      :                      SMPTE 292M data                          :      :                                                               :      |                                                               |      +---------------------------------------------------------------+          Figure 3: RTP Packet showing SMPTE 292M headers and payload5.1.  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 that designates the      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.Gharai, et al.              Standards Track                     [Page 6]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 2003   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      receivers.   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 ConsiderationsRFC 1889 should be used as specified inRFC 1889 [3], which specifies   two limits on the RTCP packet rate: RTCP bandwidth should be limited   to 5% of the data rate, and the minimum for the average of the   randomized intervals between RTCP packets should be 5 seconds.   Considering the high data rate of this payload format, the minimum   interval is the governing factor in this case.   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 the octet count and number of packets lost since   the beginning of transmission, as defined inRFC 1889.  Therefore,   for network monitoring purposes or any other application that   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.Gharai, et al.              Standards Track                     [Page 7]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 20037.  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 below:   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 inRFC 3497.   Security considerations: seeRFC 3497 section 9.   Interoperability considerations: NONE   Published specification: SMPTE292MRFC 3497   Applications which use this media type:                            Video communication.   Additional information: None   Magic number(s): None   File extension(s): None   Macintosh File Type Code(s): None   Person & email address to contact for further information:      Ladan Gharai <ladan@isi.edu>      IETF AVT working group.   Intended usage: COMMONGharai, et al.              Standards Track                     [Page 8]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 2003   Author/Change controller:         Ladan Gharai <ladan@isi.edu>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, it 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   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 if 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.Gharai, et al.              Standards Track                     [Page 9]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 200310.  Acknowledgments   We would like to thank David Richardson for his insightful comments   and contributions to the document.  We would also like to thank Chuck   Harrison for his input and for explaining the intricacies of SMPTE   292M.11.  Normative References   [1]  Society of Motion Picture and Television Engineers, Bit-Serial        Digital Interface for High-Definition Television Systems, SMPTE        292M-1998.   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement        Levels",BCP 14,RFC 2119, March 1997.   [3]  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,        "RTP: A Transport Protocol for Real-Time Applications",RFC1889, January 1996.   [4]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video        Conferences with Minimal Control",RFC 1890, January 1996.12.  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, 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,http://www.atsc.org   [11] ISO/IEC International Standard 13818-1; "Generic coding of        moving pictures and associated audio information: Systems",1996.Gharai, et al.              Standards Track                    [Page 10]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 2003   [12] Hoffman, D., Fernando, G., Goyal, V. and M. Civanlar, "RTP        Payload Format for MPEG1/MPEG2 Video",RFC 2250, 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] Handley, H. and V. Jacobson, "SDP: Session Description        Protocol",RFC 2327, April 1998.13.  Authors' Addresses   Ladan Gharai   USC/ISI   3811 Fairfax Dr.   Arlington VA 22203   EMail: ladan@isi.edu   Colin Perkins   USC/ISI   3811 Fairfax Dr.   Arlington VA 22203   EMail: csp@csperkins.org   Allison Mankin   Bell Labs, Lucent Corporation   EMail: mankin@psg.com   Gary Goncher   Tektronix, Inc.   P.O. Box 500, M/S 50-480   Beaverton, OR  97077   EMail: Gary.Goncher@tek.comGharai, et al.              Standards Track                    [Page 11]

RFC 3497        RTP Payload Format for SMPTE 292M Video       March 200314.  Full Copyright Statement   Copyright (C) The Internet Society (2003).  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 IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Gharai, et al.              Standards Track                    [Page 12]