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webm-byte-stream-format.html
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<a href="https://www.w3.org/" class="logo">
<img alt="W3C" width="72" height="48" src="https://www.w3.org/StyleSheets/TR/2016/logos/W3C">
</a>
<h1 id="title" class="title p-name">WebM Byte Stream Format</h1>
<h2 id="w3c-editor-s-draft-22-may-2018"><abbr title="World Wide Web Consortium">W3C</abbr> Editor's Draft <time class="dt-published" datetime="2018-05-22">22 May 2018</time></h2>
<dl>
<dt>This version:</dt><dd><a class="u-url" href="https://w3c.github.io/media-source/webm-byte-stream-format.html">https://w3c.github.io/media-source/webm-byte-stream-format.html</a></dd><dt>Latest published version:</dt><dd><a href="https://www.w3.org/TR/mse-byte-stream-format-webm/">https://www.w3.org/TR/mse-byte-stream-format-webm/</a></dd>
<dt>Latest editor's draft:</dt><dd><a href="https://w3c.github.io/media-source/webm-byte-stream-format.html">https://w3c.github.io/media-source/webm-byte-stream-format.html</a></dd>
<dt>Editors:</dt>
<dd class="p-author h-card vcard"><span class="p-name fn">Matthew Wolenetz</span> (<a class="p-org org h-org h-card" href="http://www.google.com/">Google Inc.</a>)</dd><dd class="p-author h-card vcard"><span class="p-name fn">Jerry Smith</span> (<a class="p-org org h-org h-card" href="http://www.microsoft.com/">Microsoft Corporation</a>)</dd><dd class="p-author h-card vcard"><span class="p-name fn">Aaron Colwell (until April 2015)</span> (<a class="p-org org h-org h-card" href="http://www.google.com/">Google Inc.</a>)</dd>
<dt>Repository:</dt><dd>
<a href="https://github.com/w3c/media-source/">We are on GitHub</a>
</dd><dd>
<a href="https://github.com/w3c/media-source/issues">File a bug</a>
</dd><dd>
<a href="https://github.com/w3c/media-source/commits/gh-pages/webm-byte-stream-format-respec.html">Commit history</a>
</dd><dt>Mailing list:</dt><dd>
<a href="https://lists.w3.org/Archives/Public/public-html-media/">public-html-media@w3.org</a>
</dd>
</dl>
<p class="copyright">
<a href="https://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> ©
2018
<a href="https://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup>
(<a href="https://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>,
<a href="https://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="https://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>).
<abbr title="World Wide Web Consortium">W3C</abbr> <a href="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a href="https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and
<a rel="license" href="https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document">permissive document license</a>
rules apply.
</p>
<hr title="Separator for header">
</div>
<section id="abstract" class="introductory"><h2 id="abstract-0">Abstract</h2>
This specification defines a <a href="index.html#">Media Source Extensions™</a> [<cite><a class="bibref" href="#bib-MEDIA-SOURCE">MEDIA-SOURCE</a></cite>] byte stream format specification based on the WebM container format.
</section>
<section id="sotd" class="introductory"><h2 id="status-of-this-document">Status of This Document</h2><p>
<em>This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current <abbr title="World Wide Web Consortium">W3C</abbr> publications and the latest revision of this technical report can be found in the <a href="https://www.w3.org/TR/"><abbr title="World Wide Web Consortium">W3C</abbr> technical reports index</a> at https://www.w3.org/TR/.</em>
</p><p>The working group maintains <a href="https://github.com/w3c/media-source/issues">a list of all bug reports that the editors have not yet tried to address</a>; there may also be open bugs in the <a href="http://w3.org/brief/Mjcw">previous bug tracker</a>.</p><p>Implementors should be aware that this specification is not stable. <strong>Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways.</strong> Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation stage should join the mailing list mentioned below and take part in the discussions.</p><p>
This document was published by the <a href="https://www.w3.org/html/wg/">HTML Media Extensions Working Group</a> as an Editor's Draft.
Comments regarding this document are welcome. Please send them to
<a href="mailto:public-html-media@w3.org">public-html-media@w3.org</a>
(<a href="mailto:public-html-media-request@w3.org?subject=subscribe">subscribe</a>,
<a href="https://lists.w3.org/Archives/Public/public-html-media/">archives</a>).
</p><p>
Publication as an Editor's Draft does not imply endorsement by the <abbr title="World Wide Web Consortium">W3C</abbr>
Membership. This is a draft document and may be updated, replaced or obsoleted by other
documents at any time. It is inappropriate to cite this document as other than work in
progress.
</p><p>
This document was produced by
a group
operating under the
<a href="https://www.w3.org/Consortium/Patent-Policy/"><abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>.
<abbr title="World Wide Web Consortium">W3C</abbr> maintains a <a rel="disclosure" href="https://www.w3.org/2004/01/pp-impl/40318/status">public list of any patent
disclosures</a>
made in connection with the deliverables of
the group; that page also includes
instructions for disclosing a patent. An individual who has actual knowledge of a patent
which the individual believes contains
<a href="https://www.w3.org/Consortium/Patent-Policy/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with
<a href="https://www.w3.org/Consortium/Patent-Policy/#sec-Disclosure">section
6 of the <abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>.
</p><p>This document is governed by the <a id="w3c_process_revision" href="https://www.w3.org/2018/Process-20180201/">1 February 2018 <abbr title="World Wide Web Consortium">W3C</abbr> Process Document</a>.
</p></section><nav id="toc"><h2 class="introductory" id="table-of-contents">Table of Contents</h2><ol class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a></li><li class="tocline"><a href="#webm-mime-parameters" class="tocxref"><span class="secno">2. </span>MIME-type parameters</a></li><li class="tocline"><a href="#webm-init-segments" class="tocxref"><span class="secno">3. </span>Initialization Segments</a></li><li class="tocline"><a href="#webm-media-segments" class="tocxref"><span class="secno">4. </span>Media Segments</a></li><li class="tocline"><a href="#webm-random-access-points" class="tocxref"><span class="secno">5. </span>Random Access Points</a></li><li class="tocline"><a href="#conformance" class="tocxref"><span class="secno">6. </span>Conformance</a></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">7. </span>Acknowledgments</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">A. </span>References</a><ol class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">A.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">A.2 </span>Informative references</a></li></ol></li></ol></nav>
<section id="introduction">
<!--OddPage--><h2 id="x1-introduction"><span class="secno">1. </span>Introduction</h2>
<p>This specification describes a byte stream format based on the WebM container format [<cite><a class="bibref" href="#bib-WEBM">WEBM</a></cite>]. It defines the MIME-type parameters used to signal codecs, and provides
the necessary format specific definitions for <a href="index.html#init-segment">initialization segments</a>, <a href="index.html#media-segment">media segments</a>, and <a href="index.html#random-access-point">random access points</a> required by
the <a href="index.html#byte-stream-formats">byte stream formats section</a> of the Media Source Extensions spec.</p>
</section>
<section id="webm-mime-parameters">
<!--OddPage--><h2 id="x2-mime-type-parameters"><span class="secno">2. </span>MIME-type parameters</h2>
<p>This section specifies the parameters that can be used in the MIME-type passed to <code><a href="index.html#dom-mediasource-istypesupported">isTypeSupported()</a></code> or <code><a href="index.html#dom-mediasource-addsourcebuffer">addSourceBuffer()</a></code>.</p>
<dl>
<dt>codecs</dt>
<dd>
A comma separated list of codec IDs used to specify what codecs will be used in the byte stream.
<table class="old-table">
<thead>
<tr>
<th>Codec ID</th>
<th>Valid with "audio/webm"</th>
<th>Valid with "video/webm"</th>
</tr>
</thead>
<tbody>
<tr>
<td>vorbis</td>
<td>true</td>
<td>true</td>
</tr>
<tr>
<td>opus</td>
<td>true</td>
<td>true</td>
</tr>
<tr>
<td>vp8</td>
<td>false</td>
<td>true</td>
</tr>
<tr>
<td>vp9</td>
<td>false</td>
<td>true</td>
</tr>
<tr>
<td>vp09... as described in the VP Codec ISO Media File Format Binding document[<cite><a class="bibref" href="#bib-VP09CODECSPARAMETERSTRING">VP09CODECSPARAMETERSTRING</a></cite>]</td>
<td>false</td>
<td>true</td>
</tr>
</tbody>
</table>
<div class="note" id="issue-container-generatedID"><div role="heading" class="note-title marker" id="h-note" aria-level="3"><span>Note</span></div><div class="">
Implementations <em class="rfc2119" title="SHOULD">SHOULD</em> support all of the codec IDs mentioned in the table above.
</div></div>
<div class="note" id="issue-container-generatedID-0"><div role="heading" class="note-title marker" id="h-note-0" aria-level="3"><span>Note</span></div><div class="">
Implementations <em class="rfc2119" title="SHOULD">SHOULD</em> encourage applications to prefer the "vp09..." codec ID over "vp9". The "vp09..." format provides detailed profile and color information, enabling implementations to give more accurate answers for codec support.
</div></div>
<p>Examples of valid MIME-types with a codecs parameter.</p>
<ul>
<li>audio/webm;codecs="vorbis"</li>
<li>video/webm;codecs="vorbis"</li>
<li>video/webm;codecs="vp8"</li>
<li>video/webm;codecs="vp8,vorbis"</li>
<li>video/webm;codecs="vp9,opus"</li>
<li>video/webm;codecs="vp09.00.10.08"</li>
<li>video/webm;codecs="vp09.02.10.10.01.09.16.09.01,opus"</li>
</ul>
</dd>
</dl>
</section>
<section id="webm-init-segments">
<!--OddPage--><h2 id="x3-initialization-segments"><span class="secno">3. </span>Initialization Segments</h2>
<p>A WebM <a href="index.html#init-segment">initialization segment</a> <em class="rfc2119" title="MUST">MUST</em> contain a subset of the elements at the start of a typical WebM file.</p>
<p>The user agent <em class="rfc2119" title="MUST">MUST</em> run the <a href="index.html#sourcebuffer-append-error">append error algorithm</a> if any of the following conditions are not met:</p>
<ol>
<li>The <a href="index.html#init-segment">initialization segment</a> <em class="rfc2119" title="MUST">MUST</em> start with an <a href="http://www.webmproject.org/docs/container/#ebml-basics">EBML Header</a> element, followed by a <a href="http://www.webmproject.org/docs/container/#segment">Segment</a> header.</li>
<li>The size value in the <a href="http://www.webmproject.org/docs/container/#segment">Segment</a> header <em class="rfc2119" title="MUST">MUST</em> signal an "unknown size" or contain a value large enough to include the <a href="http://www.webmproject.org/docs/container/#segment-information">Segment Information</a> and <a href="http://www.webmproject.org/docs/container/#track">Tracks</a> elements that follow.</li>
<li>A <a href="http://www.webmproject.org/docs/container/#segment-information">Segment Information</a> element and a <a href="http://www.webmproject.org/docs/container/#track">Tracks</a> element <em class="rfc2119" title="MUST">MUST</em> appear, in that order, after the <a href="http://www.webmproject.org/docs/container/#segment">Segment</a> header and before any further <a href="http://www.webmproject.org/docs/container/#ebml-basics">EBML Header</a> or <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a> elements.
</li>
</ol>
<p>The user agent <em class="rfc2119" title="MUST">MUST</em> accept and ignore any elements other than an <a href="http://www.webmproject.org/docs/container/#ebml-basics">EBML Header</a> or a <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a> that occur before, in between, or after the <a href="http://www.webmproject.org/docs/container/#segment-information">Segment Information</a> and
<a href="http://www.webmproject.org/docs/container/#track">Tracks</a> elements.</p>
<p>The user agent <em class="rfc2119" title="MUST">MUST</em> source attribute values for id, kind, label and language for <code><a href="https://www.w3.org/TR/html51/semantics-embedded-content.html#audiotrack-audiotrack">AudioTrack</a></code>, <code><a href="https://www.w3.org/TR/html51/semantics-embedded-content.html#videotrack-videotrack">VideoTrack</a></code> and
<code><a href="https://www.w3.org/TR/html51/semantics-embedded-content.html#texttrack-texttrack">TextTrack</a></code> objects as described for WebM in the in-band tracks spec [<cite><a class="bibref" href="#bib-INBANDTRACKS">INBANDTRACKS</a></cite>].</p>
</section>
<section id="webm-media-segments">
<!--OddPage--><h2 id="x4-media-segments"><span class="secno">4. </span>Media Segments</h2>
<p>A WebM <a href="index.html#media-segment">media segment</a> is a single <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a> element.</p>
<p>The user agent uses the following rules when interpreting content in a <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a>:</p>
<ol>
<li>The TimecodeScale in the <a href="#webm-init-segments">WebM initialization segment</a> most recently appended applies to all timestamps in the <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a></li>
<li>The Timecode element in the <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a> contains a <a href="index.html#presentation-timestamp">presentation timestamp</a> in TimecodeScale units.</li>
<li>The Cluster header <em class="rfc2119" title="MAY">MAY</em> contain an "unknown" size value. If it does then the end of the cluster is reached when another <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a> header or an element header that indicates the start
of an <a href="#webm-init-segments">WebM initialization segment</a> is encountered.</li>
</ol>
<p>The user agent <em class="rfc2119" title="MUST">MUST</em> run the <a href="index.html#sourcebuffer-append-error">append error algorithm</a> if any of the following conditions are not met:</p>
<ol>
<li>The Timecode element <em class="rfc2119" title="MUST">MUST</em> appear before any Block & SimpleBlock elements in a <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a>.</li>
<li>Block & SimpleBlock elements are in time increasing order consistent with the <a href="http://www.webmproject.org/docs/container/#webm-guidelines">WebM spec</a>.</li>
<li>If the most recent <a href="#webm-init-segments">WebM initialization segment</a> describes multiple tracks, then blocks from all the tracks <em class="rfc2119" title="MUST">MUST</em> be interleaved in time increasing order. At least one block from all audio and video
tracks <em class="rfc2119" title="MUST">MUST</em> be present.</li>
</ol>
<p>The user agent <em class="rfc2119" title="MUST">MUST</em> accept and ignore <a href="http://www.webmproject.org/docs/container/#cueing-data">Cues</a> or <a href="http://www.webmproject.org/docs/container/#chapters">Chapters</a> elements that follow a <a href="http://www.webmproject.org/docs/container/#cluster">Cluster</a> element.</p>
</section>
<section id="webm-random-access-points">
<!--OddPage--><h2 id="x5-random-access-points"><span class="secno">5. </span>Random Access Points</h2>
<p>Either a SimpleBlock element with its Keyframe flag set, or a BlockGroup element having no ReferenceBlock elements, signals the location of a <a href="index.html#random-access-point">random access point</a> for that track. The order of multiplexed blocks within a <a href="index.html#media-segment">media segment</a> <em class="rfc2119" title="MUST">MUST</em> conform to the <a href="http://www.webmproject.org/docs/container/#muxer-guidelines">WebM Muxer Guidelines</a>.</p>
</section>
<section id="conformance"><!--OddPage--><h2 id="x6-conformance"><span class="secno">6. </span>Conformance</h2><p>
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples,
and notes in this specification are non-normative. Everything else in this specification is
normative.
</p><p id="respecRFC2119">The key words <em class="rfc2119">MAY</em>, <em class="rfc2119">MUST</em>, and <em class="rfc2119">SHOULD</em> are
to be interpreted as described in [<cite><a class="bibref" href="#bib-RFC2119">RFC2119</a></cite>].
</p></section>
<section id="acknowledgements">
<!--OddPage--><h2 id="x7-acknowledgments"><span class="secno">7. </span>Acknowledgments</h2>
The editors would like to thank Chris Cunningham, Frank Galligan, and Philip Jägenstedt for their contributions to this specification.
</section>
<section id="references" class="appendix"><!--OddPage--><h2 id="a-references"><span class="secno">A. </span>References</h2><section id="normative-references"><h3 id="a-1-normative-references"><span class="secno">A.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-MEDIA-SOURCE">[MEDIA-SOURCE]</dt><dd><a href="https://www.w3.org/TR/media-source/"><cite>Media Source Extensions™</cite></a>. Matthew Wolenetz; Jerry Smith; Mark Watson; Aaron Colwell; Adrian Bateman. W3C. 17 November 2016. W3C Recommendation. URL: <a href="https://www.w3.org/TR/media-source/">https://www.w3.org/TR/media-source/</a>
</dd><dt id="bib-RFC2119">[RFC2119]</dt><dd><a href="https://tools.ietf.org/html/rfc2119"><cite>Key words for use in RFCs to Indicate Requirement Levels</cite></a>. S. Bradner. IETF. March 1997. Best Current Practice. URL: <a href="https://tools.ietf.org/html/rfc2119">https://tools.ietf.org/html/rfc2119</a>
</dd><dt id="bib-WEBM">[WEBM]</dt><dd><a href="https://www.webmproject.org/docs/container/"><cite>WebM Container Guidelines</cite></a>. The WebM Project. 26 April 2016. URL: <a href="https://www.webmproject.org/docs/container/">https://www.webmproject.org/docs/container/</a>
</dd></dl></section><section id="informative-references"><h3 id="a-2-informative-references"><span class="secno">A.2 </span>Informative references</h3><dl class="bibliography"><dt id="bib-INBANDTRACKS">[INBANDTRACKS]</dt><dd><a href="https://dev.w3.org/html5/html-sourcing-inband-tracks/"><cite>Sourcing In-band Media Resource Tracks from Media Containers into HTML</cite></a>. Bob Lund; Silvia Pfeiffer. W3C. URL: <a href="https://dev.w3.org/html5/html-sourcing-inband-tracks/">https://dev.w3.org/html5/html-sourcing-inband-tracks/</a>
</dd><dt id="bib-VP09CODECSPARAMETERSTRING">[VP09CODECSPARAMETERSTRING]</dt><dd><a href="http://www.webmproject.org/vp9/mp4/#codecs-parameter-string"><cite>VP Codec ISO Media File Format Binding</cite></a>. Frank Galligan; Kilroy Hughes; Thomás Inskip; David Ronca. WebM Project. URL: <a href="http://www.webmproject.org/vp9/mp4/#codecs-parameter-string">http://www.webmproject.org/vp9/mp4/#codecs-parameter-string</a>
</dd></dl></section></section><p role="navigation" id="back-to-top"><a href="#title"><abbr title="Back to Top">↑</abbr></a></p><script src="https://www.w3.org/scripts/TR/2016/fixup.js"></script></body></html>