Payload Working Group | J. Weaver |
Internet-Draft | BBC |
Intended status: Standards Track | December 5, 2016 |
Expires: June 8, 2017 |
RTP Payload Format for VC-2 HQ Profile Video
draft-ietf-payload-rtp-vc2hq-01
This memo describes an RTP Payload format for the High Quality (HQ) profile of SMPTE 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).
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This memo specifies an RTP payload format for the video coding standard SMPTE ST 2042-1:2012 [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 be low-complexity, and potentially have 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.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
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, the most important being 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.
The first Data Unit in a Sequence as produced by an encoder is always a Sequence Header, but sequences can be joined in the middle, so this should not be assumed.
The High Quality (HQ) profile for VC-2 restricts the types of parse info headers which may appear in the Sequence to only:
At time of writing there is currently 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.
Since there is no definition for the use of Auxiliary Data Units and Padding Data Units are defined by the VC-2 spec to be ignored by all decoders this specification only covers the transport of Sequence Headers, High Quality Pictures, and (optionally) End of Sequence headers.
Since Sequence Headers and End of Sequence Headers are always small they can easily be encapsulated in a single RTP packet each, but since High Quality Pictures are usually much larger than the MTU of most networks they require fragmentation into multiple packets.
For this reason this document defines four types of RTP packets in a VC-2 media stream: one which carries the VC-2 Sequence Header [rtp_hdr_seq], one which carries the picture fragment containing the VC-2 Transform Parameters for a Picture [rtp_hdr_preamble], one which carries a picture fragment containing VC-2 Coded Slices [rtp_hdr_slices] for a picture, and one which signals the end of a VC-2 Sequence [rtp_hdr_eos].
These four packet-types can be distinguished by the fact that they use different codes in the "PC" field, except for the two types of packet fragment which both use the same value in PC but have different values in the "No. of slices" field.
The choices of PC codes is explained in more detail in a following informative section [pc_choice].
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time Stamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | 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 Header
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time Stamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | 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
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time Stamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | 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 Slices
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time Stamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SSRC | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | contributing source (CSRC) identifiers | | .... | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | Optional Extension Header | | .... | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | Extended Sequence Number | Reserved | PC = 0x10 | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
Figure 4: RTP Payload Format For End of Sequence
The fields of the RTP header have the following additional notes on their useage:
The remaining RTP header fields are used as specified in RTP [RFC3550].
The fields of the extended headers are defined as follows:
The "PC" field in the packets is used to carry the Parse Code which identifies the type of content in the packet. For Sequence Header and End of Sequence packets this code matches the value of the Parse Code used to identify those data units in a VC-2 stream, as defined in the VC-2 specification, and each packet contains the entire such data unit.
For coded picture data, however, this is not possible because VC-2 coded picture data units are too large to fit conveniently into a packet on most transports. Rather than use the Parse Code for the picture, even though only a fragment of it is present, it was decided to create a new parse code which would indicate a fragment of a picture.
In compliance with the VC-2 specification this new choice of Parse Code preserves the meaning of all the bits given meanings in Section 10.4.1.1 of the VC-2 specification, but sets an additional bit, bit 2, which was reserved for future expansion in that specification. In this adaptation approach bit 2 now takes on the meaning of "Picture Fragment".
+----------+-----------+---------------------+---------------+ | PC (hex) | Binary | Description | Origin | +----------+-----------+---------------------+---------------+ | 0x00 | 0000 0000 | Sequence Header | VC-2 Spec | | 0x10 | 0001 0000 | End of Sequence | VC-2 Spec | +----------+-----------+---------------------+---------------+ | 0xEC | 1110 1100 | HQ Picture Fragment | This document | +----------+-----------+---------------------+---------------+
Figure 5: Parse Codes and Meanings
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. Slices = 0) the payload data MUST be the variable length coded transform parameters. This MUST NOT include the picture header (since all data in the picture header is already included in the packet header).
For the Picture Fragment packet type (PC = 0xEC and No. 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.
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 6: VC-2 Parse Info Header
To reassemble the data in the RTP packets into a valid VC-2 sequence the receiver SHOULD:
Congestion control for RTP SHALL be used in accordance with RFC 3550 [RFC3550], and with 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 [I-D.ietf-avtcore-rtp-circuit-breakers] is an update to RTP [RFC3550] that defines criteria for when one is required to stop sending RTP Packet Streams. The circuit breakers is to be implemented and followed.
This RTP payload format is identified using the video/vc2 media type which is registered in accordance with RFC 4855 [RFC4855] and using the template of RFC 6838 [RFC6838].
Type name:
Subtype name:
Required parameters:
Optional parameters: N/A
Encoding considerations:
Security considerations:
Interoperability considerations: N/A
Published specification:
Applications that use this media type:
Additional information: N/A
Person & email address to contact for further information:
Intended usage:
Restrictions on usage:
Author:
Change controller:
Provisional registration? (standards tree only):
(Any other information that the author deems interesting may be added below this line.)
The mapping of the above defined payload format media type and its parameters SHALL be done according to Section 3 of RFC 4855 [RFC4855].
All parameters are declarative.
This memo requests that IANA registers video/vc2 as specified in Section 6.1. The media type is also requested to be added to the IANA registry for "RTP Payload Format MIME types" (http://www.iana.org/assignments/rtp-parameters).
RTP packets using the payload format defined in this specification are subject to the security considerations discussed in the RTP specification [RFC3550] , and in any applicable RTP profile such as RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711] or RTP/SAVPF [RFC5124]. However, as "Securing the RTP Protocol Framework: Why RTP Does Not Mandate a Single Media Security Solution" [RFC7202] discusses, it is not an RTP payload format's responsibility to discuss or mandate what solutions are used to meet the basic security goals like confidentiality, integrity and source authenticity for RTP in general. This responsibility lays on anyone using RTP in an application. They can find guidance on available security mechanisms and important considerations in Options for Securing RTP Sessions [RFC7201]. Applications SHOULD use one or more appropriate strong security mechanisms. The rest of this security consideration section discusses the security impacting properties of the payload format itself.
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.
Note to RFC Editor: This section may be removed after carrying out all the instructions of this section.
RFCXXXX is to be replaced by the RFC number this specification receives when published.
[I-D.ietf-avtcore-rtp-circuit-breakers] | Perkins, C. and V. Singh, "Multimedia Congestion Control: Circuit Breakers for Unicast RTP Sessions", Internet-Draft draft-ietf-avtcore-rtp-circuit-breakers-18, August 2016. |
[RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
[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. |
[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. |
[RFC4855] | Casner, S., "Media Type Registration of RTP Payload Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007. |
[RFC6838] | Freed, N., Klensin, J. and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013. |
[VC2] | SMPTE, "VC-2 Video Compression", SMPTE Standard ST 2042-1, 2012. |
[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. |
[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. |
[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. |
[RFC7201] | Westerlund, M. and C. Perkins, "Options for Securing RTP Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014. |
[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. |