AVC (H.264) WebCodecs Registration

Editor’s Draft,

More details about this document
This version:
https://w3c.github.io/webcodecs/avc_codec_registration.html
Latest published version:
https://www.w3.org/TR/webcodecs-avc-codec-registration/
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Editors:
Chris Cunningham (Google Inc.)
Paul Adenot (Mozilla)
Bernard Aboba (Microsoft Corporation)
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Version History:
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Abstract

This registration is entered into the [webcodecs-codec-registry]. It describes, for AVC (H.264), the (1) fully qualified codec strings, (2) the codec-specific EncodedVideoChunk [[internal data]] bytes, (3) the VideoDecoderConfig.description bytes, (4) the values of EncodedVideoChunk [[type]], and (5) the codec-specific extensions to VideoEncoderConfig

The registration is not intended to include any information on whether a codec format is encumbered by intellectual property claims. Implementers and authors are advised to seek appropriate legal counsel in this matter if they intend to implement or use a specific codec format. Implementers of WebCodecs are not required to support the AVC / H.264 codec.

This registration is non-normative.

Status of this document

This section describes the status of this document at the time of its publication. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

Feedback and comments on this specification are welcome. GitHub Issues are preferred for discussion on this specification. Alternatively, you can send comments to the Media Working Group’s mailing-list, public-media-wg@w3.org (archives). This draft highlights some of the pending issues that are still to be discussed in the working group. No decision has been taken on the outcome of these issues including whether they are valid.

This document was published by the Media Working Group as an Editor’s Draft. The group does not expect this document to become a W3C Recommendation.

Publication as an Editor’s Draft does not imply endorsement by W3C and its Members.

The W3C Patent Policy does not carry any licensing requirements or commitments on this document.

This document is governed by the 2 November 2021 W3C Process Document.

1. Fully qualified codec strings

The codec string begins with the prefix "avc1." or "avc3.", with a suffix of 6 characters as described respectively in Section 3.4 of [rfc6381] and Section 5.4.1 of [iso14496-15].

2. EncodedVideoChunk data

EncodedVideoChunk [[internal data]] is expected to be an access unit as defined in [ITU-T-REC-H.264] section 7.4.1.2.

NOTE: An access unit contains exactly one primary coded picture.

If the bitstream is in avc format, [[internal data]] is assumed to be in canonical format, as defined in [iso14496-15] section 5.3.2.

If the bitstream is in annexb format, [[internal data]] is assumed to be in in Annex B format, as defined in [ITU-T-REC-H.264] Annex B.

NOTE: Since [[internal data]] is inherently byte-aligned, implementations are not required to recover byte-alignment.

3. VideoDecoderConfig description

If the VideoDecoderConfig.description is present, it is assumed to be an AVCDecoderConfigurationRecord, as defined by [iso14496-15], section 5.3.3.1, and the bitstream is assumed to be in avc format.

NOTE: This format is commonly used in .MP4 files, where the player generally has random access to the media data.

If the VideoDecoderConfig.description is not present, the bitstream is assumed to be in annexb format.

NOTE: "annexb" format is described in greater detail by [ITU-T-REC-H.264], Annex B. This format is commonly used in live-streaming applications, where including the SPS and PPS data periodically allows users to easily start from the middle of the stream.

4. EncodedVideoChunk type

If an EncodedVideoChunk's [[type]] is key, and the bitstream is in avc format, then the EncodedVideoChunk is expected to contain a primary coded picture that is an instantaneous decoding refresh (IDR) picture.

NOTE: If the bitstream is in avc format, parameter sets necessary for decoding are included in VideoDecoderConfig.description.

If an EncodedVideoChunk's [[type]] is key, and the bitstream is in annexb format, then the EncodedVideoChunk is expected to contain both a primary coded picture that is an instantaneous decoding refresh (IDR) picture, and all parameter sets necessary to decode all video data NAL units in the EncodedVideoChunk.

5. VideoEncoderConfig extensions

partial dictionary VideoEncoderConfig {
  AvcEncoderConfig avc;
};

avc, of type AvcEncoderConfig
Contains codec specific configuration options for the AVC (H.264) codec.

5.1. AvcEncoderConfig

dictionary AvcEncoderConfig {
  AvcBitstreamFormat format = "avc";
};

format, of type AvcBitstreamFormat, defaulting to "avc"
Configures the format of output EncodedVideoChunks. See AvcBitstreamFormat.

5.2. AvcBitstreamFormat

enum AvcBitstreamFormat {
  "annexb",
  "avc",
};

The AvcBitstreamFormat determines the location of AVC parameter sets, and mechanisms for packaging the bitstream.

annexb
SPS and PPS data are included periodically throughout the bitstream.

NOTE: This format is described in greater detail by [ITU-T-REC-H.264], Annex B. This format is commonly used in live-streaming applications, where including the SPS and PPS data periodically allows users to easily start from the middle of the stream.

avc
SPS and PPS data are not included in the bitstream and are instead emitted via the [[output callback]] as the VideoDecoderConfig.description of the EncodedVideoChunkMetadata.decoderConfig.

NOTE: This format is described in greater detail by [iso14496-15], section 5.3. This format is commonly used in .MP4 files, where the player generally has random access to the media data.

6. Privacy Considerations

Please refer to the section Privacy Considerations in [WEBCODECS].

7. Security Considerations

Please refer to the section Security Considerations in [WEBCODECS].

Conformance

Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Conformant Algorithms

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

Conformance requirements phrased as algorithms or specific steps can be implemented in any manner, so long as the end result is equivalent. In particular, the algorithms defined in this specification are intended to be easy to understand and are not intended to be performant. Implementers are encouraged to optimize.

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://datatracker.ietf.org/doc/html/rfc2119
[WEBCODECS]
Chris Cunningham; Paul Adenot; Bernard Aboba. WebCodecs. URL: https://w3c.github.io/webcodecs/

Informative References

[ISO14496-15]
ISO/IEC 14496-15:2019 Information technology — Coding of audio-visual objects — Part 15: Carriage of network abstraction layer (NAL) unit structured video in the ISO base media file format. September 2019. URL: https://www.iso.org/standard/74429.html
[ITU-T-REC-H.264]
H.264 : Advanced video coding for generic audiovisual services. June 2019. URL: https://www.itu.int/rec/T-REC-H.264
[RFC6381]
R. Gellens; D. Singer; P. Frojdh. The 'Codecs' and 'Profiles' Parameters for "Bucket" Media Types. August 2011. Proposed Standard. URL: https://www.rfc-editor.org/rfc/rfc6381
[WEBCODECS-CODEC-REGISTRY]
Chris Cunningham; Paul Adenot; Bernard Aboba. WebCodecs Codec Registry. URL: https://w3c.github.io/webcodecs/codec_registry.html

IDL Index

partial dictionary VideoEncoderConfig {
  AvcEncoderConfig avc;
};


dictionary AvcEncoderConfig {
  AvcBitstreamFormat format = "avc";
};


enum AvcBitstreamFormat {
  "annexb",
  "avc",
};