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Internet Engineering Task Force (IETF)                         J. WeaverRequest for Comments: 8450                                           BBCCategory: Standards Track                                   October 2018ISSN: 2070-1721RTP Payload Format for VC-2 High Quality (HQ) ProfileAbstract   This memo describes an RTP payload format for the High Quality (HQ)   profile of Society of Motion Picture and Television Engineers   Standard ST 2042-1, known as VC-2.  This document describes the   transport of HQ Profile VC-2 in RTP packets and has applications for   low-complexity, high-bandwidth streaming of both lossless and lossy   compressed video.   The HQ profile of VC-2 is intended for low-latency video compression   (with latency potentially on the order of lines of video) at high   data rates (with compression ratios on the order of 2:1 or 4:1).Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8450.Weaver                       Standards Track                    [Page 1]

RFC 8450                   VC-2 HQ RTP Payload              October 2018Copyright Notice   Copyright (c) 2018 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (https://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Conventions, Definitions, and Acronyms  . . . . . . . . . . .33.  Media Format Description  . . . . . . . . . . . . . . . . . .34.  Payload Format  . . . . . . . . . . . . . . . . . . . . . . .44.1.  RTP Header Usage  . . . . . . . . . . . . . . . . . . . .104.2.  Payload Header  . . . . . . . . . . . . . . . . . . . . .114.3.  The Choice of Parse Codes (Informative) . . . . . . . . .134.4.  Stream Constraints  . . . . . . . . . . . . . . . . . . .144.5.  Payload Data  . . . . . . . . . . . . . . . . . . . . . .154.5.1.  Reassembling the Data . . . . . . . . . . . . . . . .165.  Forward Error Correction (FEC) Considerations . . . . . . . .186.  Congestion Control Considerations . . . . . . . . . . . . . .187.  Payload Format Parameters . . . . . . . . . . . . . . . . . .197.1.  Media Type Definition . . . . . . . . . . . . . . . . . .197.2.  Mapping to the Session Description Protocol (SDP) . . . .217.3.  Offer/Answer Considerations . . . . . . . . . . . . . . .218.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .219.  Security Considerations . . . . . . . . . . . . . . . . . . .2110. References  . . . . . . . . . . . . . . . . . . . . . . . . .2210.1.  Normative References . . . . . . . . . . . . . . . . . .2210.2.  Informative References . . . . . . . . . . . . . . . . .23   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .24Weaver                       Standards Track                    [Page 2]

RFC 8450                   VC-2 HQ RTP Payload              October 20181.  Introduction   This memo specifies an RTP payload format for the video coding   standard Society of Motion Picture and Television Engineers ST   2042-1:2017 [VC2], also known as VC-2   The VC-2 codec is a wavelet-based codec intended primarily for   professional video use with high bit-rates and only low levels of   compression.  It has been designed to have a low level of complexity   and potentially a very low latency through both encoder and decoder:   with some choices of parameters, this latency may be as low as a few   lines of video.   The low level of complexity in the VC-2 codec allows for this low-   latency operation but also means that it lacks many of the more   powerful compression techniques used in other codecs.  As such, it is   suitable for low compression ratios that produce coded data rates   around half to a quarter of that of uncompressed video, at a similar   visual quality.   The primary use for VC-2 is likely to be in professional video   production environments.2.  Conventions, Definitions, and Acronyms   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.3.  Media Format Description   The VC-2 specification defines a VC-2 Stream as being composed of one   or more Sequences.  Each Sequence is independently decodable,   containing all of the needed parameters and metadata for configuring   the decoder.   Each Sequence consists of a series of 13-octet Parse Info Headers and   variable-length Data Units.  The Sequence begins and ends with a   Parse Info Header, and each Data Unit is preceded by a Parse Info   Header.  Data Units come in a variety of types, and the type of a   Data Unit is signaled in the preceding Parse Info Header.  The most   important types are the Sequence Header, which contains configuration   data needed by the decoder, and several types of Coded Picture, which   contain the coded data for the pictures themselves.  Each picture   represents a frame in a progressively scanned video Sequence or a   field in an interlaced video Sequence.Weaver                       Standards Track                    [Page 3]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   The first Data Unit in a Sequence as produced by an encoder is always   a Sequence Header; however, Sequences can be joined in the middle, so   it should not be assumed that the first Data Unit received will   always be a Sequence Header.   The High Quality (HQ) profile for VC-2 restricts the types of Parse   Info Headers that may appear in the Sequence (and hence also the   types of Data Unit) to only:   o  Sequence Headers (which are always followed by a Data Unit),   o  High Quality Pictures (which are always followed by a Data Unit),   o  High Quality Fragments (which are always followed by a Data Unit),   o  Auxiliary Data (which are always followed by a Data Unit),   o  Padding Data (which are always followed by a Data Unit), and   o  End of Sequence (which are never followed by a Data Unit).   At the time of writing, there is no definition for the use of   Auxiliary Data in VC-2, and Padding Data is required to be ignored by   all receivers.   Each High Quality Picture Data Unit contains a set of parameters for   the picture followed by a series of Coded Slices, each representing a   rectangular region of the transformed picture.  Slices within a   picture may vary in coded length, but all represent the same shape   and size of rectangle in the picture.   Each High Quality Fragment Data Unit contains either a set of   parameters for a picture or a series of Coded Slices.  Fragments   carry the same data as pictures, but broken up into smaller units to   facilitate transmission via packet-based protocols such as RTP.   This payload format only makes use of Fragments, not pictures.4.  Payload Format   In this specification, each RTP packet is used to carry data   corresponding to a single Parse Info Header and its following Data   Unit (if it has one).  A single packet MAY NOT contain data from more   than one Parse Info Header or Data Unit.  A single Parse Info Header   and Data Unit pair MUST NOT be split across more than one packet.   The sole exception to this rule is that an Auxiliary Data Unit MAY be   split between multiple packets, using the B and E flags to indicate   start and end.Weaver                       Standards Track                    [Page 4]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   This specification only covers the transport of Sequence Headers   (together with their accompanying Data Unit), High Quality Fragments   (together with their accompanying Data Unit), Auxiliary Data   (together with their accompanying Data Unit), and (optionally) End   Sequence Headers and Padding Data (for which no Data Unit it   carried).   High Quality Pictures can be transported by converting them into an   equivalent set of High Quality Fragments.  The size of Fragments   should be chosen so as to fit within the MTU of the network in use.   For this reason, this document defines six types of RTP packets in a   VC-2 media stream:   o  a VC-2 Sequence Header (Figure 1) (seeSection 11 of the VC-2      specification [VC2]),   o  a Picture Fragment containing the VC-2 Transform Parameters for a      Picture (Figure 2) (seeSection 14 of the VC-2 specification      [VC2]),   o  a Picture Fragment containing VC-2 Coded Slices (Figure 3) for a      picture (seeSection 14 of the VC-2 specification [VC2]),   o  the end of a VC-2 Sequence (Figure 4) (seeSection 10.5.2 of the      VC-2 specification [VC2]),   o  the contents of an Auxiliary Data Unit (Figure 5) (seeSection 10.4.4 of the VC-2 specification [VC2]), and   o  an indication of the presence of a padding Data Unit (Figure 6)      (seeSection 10.4.5 of the VC-2 specification [VC2]).   These six packet types can be distinguished by the fact that they use   different codes in the Parse Code ("PC") field, except for the two   types of Picture Fragment that use the same value in PC but have   different values in the "No. of Slices" field.   The options for PC codes are explained in more detail inSection 4.3.Weaver                       Standards Track                    [Page 5]

RFC 8450                   VC-2 HQ RTP Payload              October 2018    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 Number         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Timestamp                           |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |           synchronization source (SSRC) identifier            |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |            contributing source (CSRC) identifiers             |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |                 Optional Extension Header                     |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |   Extended Sequence Number    |    Reserved   |   PC = 0x00   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   .                                                               .   .               Variable-Length Coded Sequence Header           .   .                                                               .   +---------------------------------------------------------------+             Figure 1: RTP Payload Format for Sequence HeaderWeaver                       Standards Track                    [Page 6]

RFC 8450                   VC-2 HQ RTP Payload              October 2018    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 Number         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Timestamp                           |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |           synchronization source (SSRC) identifier            |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |            contributing source (CSRC) identifiers             |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |                 Optional Extension Header                     |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |   Extended Sequence Number    |  Reserved |I|F|   PC = 0xEC   |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |                       Picture Number                          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   |       Slice Prefix Bytes      |        Slice Size Scaler      |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   |       Fragment Length         |         No. of Slices = 0     |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   .                                                               .   .         Variable-Length Coded Transform Parameters            .   .                                                               .   +---------------------------------------------------------------+      Figure 2: RTP Payload Format for Transform Parameters FragmentWeaver                       Standards Track                    [Page 7]

RFC 8450                   VC-2 HQ RTP Payload              October 2018    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 Number         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Timestamp                           |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |           synchronization source (SSRC) identifier            |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |            contributing source (CSRC) identifiers             |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |                 Optional Extension Header                     |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |   Extended Sequence Number    |  Reserved |I|F|   PC = 0xEC   |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |                       Picture Number                          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   |       Slice Prefix Bytes      |        Slice Size Scaler      |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   |       Fragment Length         |          No. of Slices        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   |        Slice Offset X         |         Slice Offset Y        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   .                                                               .   .                          Coded Slices                         .   .                                                               .   +---------------------------------------------------------------+        Figure 3: RTP Payload Format for Fragment Containing SlicesWeaver                       Standards Track                    [Page 8]

RFC 8450                   VC-2 HQ RTP Payload              October 2018    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 Number         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Timestamp                           |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |           synchronization source (SSRC) identifier            |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |            contributing source (CSRC) identifiers             |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |                 Optional Extension Header                     |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |   Extended Sequence Number    |    Reserved   |   PC = 0x10   |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+             Figure 4: RTP Payload Format for End of Sequence    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 Number         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Timestamp                           |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |           synchronization source (SSRC) identifier            |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |            contributing source (CSRC) identifiers             |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |                 Optional Extension Header                     |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |   Extended Sequence Number    |B|E|  Reserved |   PC = 0x20   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Data Length                         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   .                                                               .   .                      Uncoded Payload Data                     .   .                                                               .   +---------------------------------------------------------------+              Figure 5: RTP Payload Format for Auxiliary DataWeaver                       Standards Track                    [Page 9]

RFC 8450                   VC-2 HQ RTP Payload              October 2018    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 Number         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Timestamp                           |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |           synchronization source (SSRC) identifier            |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |            contributing source (CSRC) identifiers             |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |                 Optional Extension Header                     |   |                             ....                              |   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+   |   Extended Sequence Number    |B|E|  Reserved |   PC = 0x30   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                           Data Length                         |   +---------------------------------------------------------------+               Figure 6: RTP Payload Format for Padding Data   All fields in the headers longer than a single bit are interpreted as   unsigned integers in network byte order.4.1.  RTP Header Usage   The fields of the RTP header have the following additional notes on   their usage:   Marker Bit (M): 1 bit.  The marker bit MUST be set on any packet that         contains the final slice in a coded picture and MUST NOT be set         otherwise.   Payload Type (PT): 7 bits.  A dynamically allocated payload type         field that designates the payload as VC-2-coded video.   Sequence Number: 16 bits.  Because the data rate of VC-2-coded         Streams can often be very high, in the order of gigabits rather         than megabits per second, the standard 16-bit RTP sequence         number can cycle very quickly.  For this reason, the sequence         number is extended to 32 bits, and this field MUST hold the         low-order 16 bits of this value.Weaver                       Standards Track                   [Page 10]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   Timestamp: 32 bits.  If the packet contains Transform Parameters or         Coded Slice data for a coded picture, then the timestamp         corresponds to the sampling instant of the coded picture.  A         90kHz clock SHOULD be used.  A single RTP packet MUST NOT         contain coded data for more than one coded picture, so there is         no ambiguity here.         A Sequence Header packet SHOULD have the same timestamp as the         picture that will follow it in the Stream.  An End of Sequence         packet SHOULD have the same timestamp as the previous picture         that appeared in the Stream.   The remaining RTP header fields are used as specified in RTP   [RFC3550].4.2.  Payload Header   The fields of the extended headers are defined as follows:   Extended Sequence Number: 16 bits.  MUST contain the high-order 16         bits of the 32-bit packet sequence number.  This is needed         since the high data rates of VC-2 Sequences mean that it is         highly likely that the 16-bit sequence number will roll over         too frequently to be of use for Stream synchronization.   B: 1 bit.  MUST be set to 1 if the packet contains the first byte of         an Auxiliary Data Unit and otherwise MUST be 0.  If the         recommendations inSection 4.4 ("Stream Constraints") are         followed, then every Auxiliary Data Unit will be small enough         to fit in a single packet, and so this bit (where present) will         always be 1.   E: 1 bit.  MUST be set to 1 if the packet contains the final byte of         an Auxiliary Data Unit and otherwise MUST be 0.  If the         recommendations inSection 4.4 ("Stream Constraints") are         followed, then every Auxiliary Data Unit will be small enough         to fit in a single packet, and so this bit (where present) will         always be 1.   I: 1 bit.  MUST be set to 1 if the packet contains coded picture         parameters or slice data from a field in an interlaced frame.         MUST be set to 0 if the packet contains data from any part of a         progressive frame.Weaver                       Standards Track                   [Page 11]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   F: 1 bit.  MUST be set to 1 if the packet contains coded picture         parameters or slice data from the second field of an interlaced         frame.  MUST be set to 0 if the packet contains data from the         first field of an interlaced frame or any part of a progressive         frame.   Parse Code (PC): 8 bits.  Contains a Parse Code that MUST be the         value indicated for the type of data in the packet.   Data Length: 32 bits.  For an auxiliary Data Unit, this contains the         number of bytes of data contained in the payload section of         this packet.  If the recommendations inSection 4.4 ("Stream         Constraints") are followed, then no Auxiliary Data Unit will be         large enough to cause a packet to exceed the MTU of the         network.   Picture Number: 32 bits.  MUST contain the Picture Number for the         coded picture this packet contains data for, as described inSection 12.1 of the VC-2 specification [VC2].         The sender MUST send at least one transform-parameters packet         for each coded picture and MAY include more than one as long as         they contain identical data.  The sender MUST NOT send a packet         from a new picture until all the coded data from the current         picture has been sent.         If the receiver receives Coded Slices packets for a picture but         does not receive a Transform Parameters packet for that         picture, then this is an indication of either packet loss,         joining a Stream mid-picture, or a non-compliant transmitter.         In this case, the receiver MAY assume that the parameters are         unchanged since the last picture, or it MAY discard the         picture.  Choosing between these two options is left up to the         implementation as it will be dependent on intended use.  The         former may result in malformed pictures, while the latter will         result in dropped frames.   Slice Prefix Bytes: 16 bits.  MUST contain the Slice Prefix Bytes         value for the coded picture this packet contains data for, as         described inSection 12.3.4 of the VC-2 specification [VC2].         In the VC-2 specification, this value is not restricted to 16         bits, but the constraints on Streams specified in this document         (Section 4.4) do require this.Weaver                       Standards Track                   [Page 12]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   Slice Size Scaler: 16 bits.  MUST contain the Slice Size Scaler value         for the coded picture this packet contains data for, as         described inSection 12.3.4 of the VC-2 specification [VC2].         In the VC-2 specification, this value is not restricted to 16         bits, but the constraints on Streams specified in this document         (Section 4.4) do require this.   Fragment Length: 16 bits.  MUST contain the number of bytes of data         contained in the coded payload section of this packet.   No. of Slices: 16 bits.  MUST contain the number of Coded Slices         contained in this packet, which MUST be 0 for a packet         containing Transform Parameters.  In a packet containing Coded         Slices, this number MUST be the number of whole slices         contained in the packet, and the packet MUST NOT contain any         partial slices.   Slice Offset X: 16 bits.  MUST contain the X coordinate of the first         slice in this packet, in slices, starting from the top left         corner of the picture.   Slice Offset Y: 16 bits.  MUST contain the Y coordinate of the first         slice in this packet, in slices, starting from the top left         corner of the picture.4.3.  The Choice of Parse Codes (Informative)   The "PC" field in the packets is used to carry the Parse Code, which   identifies the type of content in the packet.  This code matches the   value of the Parse Code used to identify each Data Unit in a VC-2   Stream, as defined in the VC-2 specification, and each packet   contains the entire Data Unit.   Figure 7 lists all of the Parse Codes currently allowed in a VC-2   Sequence.  The final column indicates whether the code in question   can be present in a Stream transmitted using this specification.Weaver                       Standards Track                   [Page 13]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   +----------+-----------+---------------------+---------------+   | PC (hex) | Binary    | Description         | Valid         |   +----------+-----------+---------------------+---------------+   | 0x00     | 0000 0000 | Sequence Header     | Yes           |   | 0x10     | 0001 0000 | End of Sequence     | Yes           |   | 0x20     | 0010 0000 | Auxiliary Data      | Yes           |   | 0x30     | 0011 0000 | Padding Data        | Yes           |   +----------+-----------+---------------------+---------------+   | 0xC8     | 1100 1000 | LD Picture          | No            |   | 0xE8     | 1110 1000 | HQ Picture          | No            |   | 0xEC     | 1110 1100 | HQ Picture Fragment | Yes           |   +----------+-----------+---------------------+---------------+                    Figure 7: Parse Codes and Meanings4.4.  Stream Constraints   A Sequence needs to conform to certain constraints in order to be   transmissible with this specification.   o  The Sequence MUST NOT contain Parse Info Headers with a Parse Code      other than 0x00 (Sequence Header), 0x10 (End of Sequence), 0x20      (Auxiliary Data), 0x30 (Padding Data), or 0xEC (High Quality      Picture Fragment).  Some other Streams MAY be convertible to meet      this restriction (see below).   o  Every High Quality Picture Fragment MUST be no longer than 65535      bytes.  This can usually be ensured by splitting large Fragments      into several smaller Fragments, except in the case where an      individual slice is too large, in which case see the notes below      on conversion.   o  Informative note: this requirement ensures that every High Quality      Picture Fragment will always contain no more than 65535 slices.   o  Every High Quality Picture Fragment SHOULD be small enough that      the RTP packet carrying it will fit within the network MTU size.      This can usually be ensured by splitting large Fragments into      several smaller Fragments, except in the case where an individual      slice is too large, in which case see the notes below on      conversion.   o  Every High Quality Picture Fragment MUST be encoded using values      for Slice Prefix Bytes and Slice Size Scaler no greater than      65535.Weaver                       Standards Track                   [Page 14]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   If a Sequence intended for transmission does not conform to these   restrictions, then it MAY be possible to simply convert it into a   form that does by splitting pictures and/or large Fragments into   suitably sized Fragments.  This can be done provided that the   following (weaker) constraints are met:   o  The Sequence does not contain Parse Info Headers with a Parse Code      other than 0x00 (Sequence Header), 0x10 (End of Sequence), 0x20      (Auxiliary Data), 0x30 (Padding Data), 0xE8 (High Quality      Picture), or 0xEC (High Quality Picture Fragment).   o  None of the High Quality Pictures or High Quality Picture      Fragments contain slices that are individually longer than 65535      bytes.  Note: When this is the case, the values of Slice Prefix      Bytes and Slice Size Scaler will necessarily also be smaller than      65535.   o  None of the High Quality Pictures or High Quality Picture      Fragments contain slices that are individually so large that an      RTP packet carrying a Fragment containing that single slice will      fit within the network MTU size.   It is not possible to send a Stream that does not meet the above   requirements via this mechanism unless the Stream is re-encoded by a   VC-2 Encoder so as to meet them.   In addition, every Auxiliary Data Unit SHOULD be small enough that a   single RTP packet carrying it will fit within the network MTU size.   Since there is currently no specification for the format of Auxiliary   Data in VC-2, the mechanism for ensuring this with an encoder   implementation that includes Auxiliary Data Units will be dependent   upon the implementation's use for them.   When encoding VC-2 video intended to be transported via RTP, a VC-2   profile and level that ensures these requirements are met SHOULD be   used.4.5.  Payload Data   For the Sequence Header packet type (PC = 0x00), the payload data   MUST be the coded Sequence Header exactly as it appears in the VC-2   Sequence.   For the Transform Parameters packet type (PC = 0xEC and No. of Slices   = 0), the payload data MUST be the variable-length coded Transform   Parameters.  This MUST NOT include the Fragment header (since all   data in the picture header is already included in the packet header).Weaver                       Standards Track                   [Page 15]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   For the Auxiliary Data packet type (PC = 0x20), the payload data MUST   be a portion of the auxiliary data bytes contained in the Auxiliary   Data Unit being transmitted.  The B flag MUST be set on the packet   that contains the first byte, the E flag MUST be set on the packet   that contains the last byte, the bytes MUST be included in order, and   the packets MUST have contiguous sequence numbers.   For the Picture Fragment packet type (PC = 0xEC and No. of Slices >   0), the payload data MUST be a specified number of Coded Slices in   the same order that they appear in the VC-2 Stream.  Which slices   appear in the packet is identified using the Slice Offset X and Slice   Offset Y fields in the payload header.   For the End of Sequence packet type (PC = 0x10), there is no payload   data.4.5.1.  Reassembling the Data     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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |      0x42     |      0x42     |      0x43     |      0x44     |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Parse Code   |                       Next Parse Offset   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                   |                       Prev Parse Offset   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                   |   +-+-+-+-+-+-+-+-+                     Figure 8: VC-2 Parse Info Header   To reassemble the data in the RTP packets into a valid VC-2 Sequence:   o  The receiver SHOULD take the data from each packet with a Parse      Code of 0x00 and prepend a valid VC-2 Parse Info Header (Figure 8)      with the same Parse Code (0x00).  The resulting Sequence Header      Parse Info Header and Data Unit MUST be included in the output      stream before any coded pictures that followed the packet being      processed in the RTP stream, unless an identical Sequence Header      has already been included, and they MAY be repeated (with      appropriate modifications to the next and previous header offsets)      at any point that results in a valid VC-2 Stream.Weaver                       Standards Track                   [Page 16]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   o  The receiver SHOULD take the data from each packet with a Parse      Code of 0xEC and No. of Slices set to 0 (which together indicate      that this packet contains the Transform Parameters for a coded      picture) and prepend with the same Parse Code a valid VC-2 Parse      Info Header (Figure 8) followed by the picture number, Fragment      data length, and slice count (0).   o  The receiver SHOULD take the data from each packet with a Parse      Code of 0xEC and No. of Slices not set to 0 (which together      indicate that this packet contains Coded Slices) and prepend with      the same Parse Code a valid VC-2 Parse Info Header (Figure 8)      followed by the picture number, Fragment data length, slice count,      x offset and y offset taken from the packet header.   o  A receiver MAY combine all Fragment Data Units (with Parse Code      0xEC) and the same picture number into a single picture Data Unit      with Parse Code 0xE8.  If the Stream is required to comply with      major versions 1 or 2 of the VC-2 specification, then this MUST be      done.   o  The receiver SHOULD take the data from each packet with a Parse      Code of 0x20 and the B bit set and prepend a valid VC-2 Parse Info      Header (Figure 8) with the Parse Code 0x20, and then take each      subsequent packet with Parse Code 0x20 without the B bit set and      append its payload to the growing Data Unit.  When all packets for      a particular Data Unit have been received, it SHOULD be included      in the output stream.  The final packet for a Data Unit will have      the E bit set.   o  Once a Data Unit has been assembled, whether a Sequence Header,      Coded Picture Fragment, Coded Picture, or Auxiliary Data Unit, the      next parse offset and previous parse offset values in its Parse      Info Header SHOULD be filled with the offset between the start of      the header and the start of the next or previous header.   o  An End of Sequence Parse Info Header MAY be inserted when a packet      with Parse Code set to 0x10 is encountered, or at any other time      that is allowed in a valid VC-2 Stream.  After an End of Sequence      Parse Info Header is included in the output stream, either the      Stream must end, or it MUST be followed by a Sequence Header      indicating the start of a new Sequence.  The next parse offset of      the End of Sequence header MUST be set to 0, and the previous      parse offset SHOULD be filled with the offset from the start of      the previous Parse Info Header in the Stream.   o  A Padding Data Parse Info Header MAY be inserted when a packet      with Parse Code set to 0x30 and the B bit set is encountered, or      at any other time that is allowed in a valid VC-2 Stream.  TheWeaver                       Standards Track                   [Page 17]

RFC 8450                   VC-2 HQ RTP Payload              October 2018      length of the accompanying Data Unit MAY have any value, and its      contents MUST be set to a series of zero bytes.  The next parse      offset and previous parse offset values in its Parse Info Header      SHOULD be filled with the offset between the start of the header      and the start of the next or previous header.5.  Forward Error Correction (FEC) Considerations   VC-2 provides no underlying protection against data loss, so it may   be useful to employ Forward Error Correction to the Stream.  A   mechanism for doing this to a generic RTP stream is specified inRFC5109 [RFC5109].  If making use of this mechanism to provide   multilevel protection, then the packets SHOULD be assigned to layers   based upon their packet type, with the packet types being, in order   of importance:   1.  Sequence Headers   2.  Fragments containing Transform Parameters   3.  Fragments containing Coded Slices   4.  Auxiliary Data and end of Sequence   5.  Padding   It is RECOMMENDED that if multilevel protection is to be used, then   one layer will protect all Sequence Header packets, and a second will   protect Sequence Headers and all Fragments.  If desired, a third   layer MAY protect Auxiliary Data and End of Sequence packets.   Padding data SHOULD NOT be protected by FEC.6.  Congestion Control Considerations   Congestion control for RTP SHALL be used in accordance withRFC 3550   [RFC3550] and any applicable RTP profile -- e.g.,RFC 3551 [RFC3551].   An additional requirement if best-effort service is being used is:   users of this payload format MUST monitor packet loss to ensure that   the packet loss rate is within acceptable parameters.  Circuit   Breakers [RFC8083] are an update to RTP [RFC3550] that defines   criteria for when one is required to stop sending RTP Packet Streams,   and applications implementing this standard MUST comply with it.RFC8085 [RFC8085] provides additional information on the best practices   for applying congestion control to UDP streams.Weaver                       Standards Track                   [Page 18]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   In particular, it should be noted that the expected data rate for RTP   sessions that use this profile is likely to be in the range of   gigabits per second.  If used on a closed network that has been   correctly provisioned for the expected data rates, this might not   pose a problem, but there is always the risk of data getting out onto   the open internet.7.  Payload Format Parameters   This RTP payload format is identified using the 'video/vc2' media   type, which is registered in accordance withRFC 4855 [RFC4855],   using the template ofRFC 6838 [RFC6838].7.1.  Media Type Definition   Type name:      video   Subtype name:      vc2   Required parameters:      rate: The RTP timestamp clock rate.  Applications using this      payload format SHOULD use a value of 90000.      profile: The VC-2 profile in use.  The only value currently      allowed is "HQ".   Optional parameters:      version: the VC-2 specification version in use.  The only      currently allowed value is "3" since all Sequences transported      using this mechanism will contain HQ Picture Fragment Data Units,      which the VC-2 specification [VC2] defines as requiring version 3.      level: The VC-2 level in use.  Any integer may be used.   Encoding considerations:      This media type is framed and binary; seeSection 4.8 in RFC 6838      [RFC6838].   Security considerations:      Please see the security considerations inRFC 8450.Weaver                       Standards Track                   [Page 19]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   Interoperability considerations: N/A   Published specification:RFC 8450   Applications that use this media type:      Video Communication.   Fragment identifier considerations: N/A   Additional information: N/A   Person & email address to contact for further information:      James P. Weaver <james.barrett@bbc.co.uk>   Intended usage:      COMMON   Restrictions on usage:      This media type depends on RTP framing and hence is only defined      for transfer via RTP [RFC3550].  Transport within other framing      protocols is not defined at this time.   Author:      James P. Weaver <james.barrett@bbc.co.uk>   Change controller:      IETF PAYLOAD Working Group delegated from the IESG.   Provisional registration? (standards tree only):      NoWeaver                       Standards Track                   [Page 20]

RFC 8450                   VC-2 HQ RTP Payload              October 20187.2.  Mapping to the Session Description Protocol (SDP)   The mapping of the above-defined payload format media type and its   parameters SHALL be done according toSection 3 of RFC 4855   [RFC4855].   o  The type name ("video") goes in SDP "m=" as the media name.   o  The subtype name ("vc2") goes in SDP "a=rtpmap" as the encoding      name, followed by a slash ("/") and the rate parameter.   o  The required parameter profile and the optional parameters version      and level, when present, are included in the "a=fmtp" attribute      line of SDP as a semicolon-separated list of parameter=value      pairs.   Version and level SHALL be specified in decimal when present.   For example, a sample SDP mapping for VC-2 could be as follows:             m=video 30000 RTP/AVP 112             a=rtpmap:112 vc2/90000             a=fmtp:112 profile=HQ;version=3;level=0   In this example, a dynamic payload type 112 is used for vc-2 data.   The 90 kHz RTP timestamp rate is specified in the "a=rtpmap" line   after the subtype.  In the "a=fmtp:" line, profile HQ, version 3, and   level 0 (unknown or non-standard level) are specified.7.3.  Offer/Answer Considerations   All parameters are declarative.8.  IANA Considerations   IANA has registered 'video/vc2' as specified inSection 7.1.  The   media type has been added to the IANA registry for "RTP Payload   Format Media Types"   <https://www.iana.org/assignments/rtp-parameters>.9.  Security Considerations   RTP packets using the payload format defined in this specification   are subject to the security considerations discussed in the RTP   specification [RFC3550] and any applicable RTP profile such as   RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711], or   RTP/SAVPF [RFC5124].  However, as "Securing the RTP Framework: Why   RTP Does Not Mandate a Single Media Security Solution" [RFC7202]Weaver                       Standards Track                   [Page 21]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   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 lies with anyone using RTP in an   application.  They can find guidance on available security mechanisms   and important considerations in "Options for Securing RTP Sessions"   [RFC7201].  Applications SHOULD use one or more appropriate strong   security mechanisms.  The rest of this section discusses the   security-impacting properties of the payload format itself.   This RTP payload format and its media decoder do not exhibit any   significant non-uniformity in the receiver-side computational   complexity for packet processing and thus are unlikely to pose a   denial-of-service threat due to the receipt of pathological data.   Nor does the RTP payload format contain any active content.   To avoid buffer overruns when processing these packets, the receiver   MUST consider both the reported Fragment length and the actual   received size of a packet containing slice data.   In some cases, the transmitter may need to decode variable-length   coded headers in order to extract some data from the VC-2 bitstream   before assembling packets.  This process is potentially subject to   buffer overruns if not implemented carefully.10.  References10.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.              Jacobson, "RTP: A Transport Protocol for Real-Time              Applications", STD 64,RFC 3550, DOI 10.17487/RFC3550,              July 2003, <https://www.rfc-editor.org/info/rfc3550>.   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and              Video Conferences with Minimal Control", STD 65,RFC 3551,              DOI 10.17487/RFC3551, July 2003,              <https://www.rfc-editor.org/info/rfc3551>.   [RFC4855]  Casner, S., "Media Type Registration of RTP Payload              Formats",RFC 4855, DOI 10.17487/RFC4855, February 2007,              <https://www.rfc-editor.org/info/rfc4855>.Weaver                       Standards Track                   [Page 22]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type              Specifications and Registration Procedures",BCP 13,RFC 6838, DOI 10.17487/RFC6838, January 2013,              <https://www.rfc-editor.org/info/rfc6838>.   [RFC8083]  Perkins, C. and V. Singh, "Multimedia Congestion Control:              Circuit Breakers for Unicast RTP Sessions",RFC 8083,              DOI 10.17487/RFC8083, March 2017,              <https://www.rfc-editor.org/info/rfc8083>.   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage              Guidelines",BCP 145,RFC 8085, DOI 10.17487/RFC8085,              March 2017, <https://www.rfc-editor.org/info/rfc8085>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC2119 Key Words",BCP 14,RFC 8174, DOI 10.17487/RFC8174,              May 2017, <https://www.rfc-editor.org/info/rfc8174>.   [VC2]      SMPTE, "SMPTE Standard - VC-2 Video Compression",              ST 2042-1:2017, DOI 10.5594/SMPTE.ST2042-1.2017, June              2017, <https://ieeexplore.ieee.org/servlet/opac?punumber=7967894>.10.2.  Informative References   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.              Norrman, "The Secure Real-time Transport Protocol (SRTP)",RFC 3711, DOI 10.17487/RFC3711, March 2004,              <https://www.rfc-editor.org/info/rfc3711>.   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,              "Extended RTP Profile for Real-time Transport Control              Protocol (RTCP)-Based Feedback (RTP/AVPF)",RFC 4585,              DOI 10.17487/RFC4585, July 2006,              <https://www.rfc-editor.org/info/rfc4585>.   [RFC5109]  Li, A., Ed., "RTP Payload Format for Generic Forward Error              Correction",RFC 5109, DOI 10.17487/RFC5109, December              2007, <https://www.rfc-editor.org/info/rfc5109>.   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for              Real-time Transport Control Protocol (RTCP)-Based Feedback              (RTP/SAVPF)",RFC 5124, DOI 10.17487/RFC5124, February              2008, <https://www.rfc-editor.org/info/rfc5124>.   [RFC7201]  Westerlund, M. and C. Perkins, "Options for Securing RTP              Sessions",RFC 7201, DOI 10.17487/RFC7201, April 2014,              <https://www.rfc-editor.org/info/rfc7201>.Weaver                       Standards Track                   [Page 23]

RFC 8450                   VC-2 HQ RTP Payload              October 2018   [RFC7202]  Perkins, C. and M. Westerlund, "Securing the RTP              Framework: Why RTP Does Not Mandate a Single Media              Security Solution",RFC 7202, DOI 10.17487/RFC7202, April              2014, <https://www.rfc-editor.org/info/rfc7202>.Author's Address   James P. Weaver   BBC   Email: james.barrett@bbc.co.ukWeaver                       Standards Track                   [Page 24]