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<title>Sourcing In-band Media Resource Tracks from Media Containers into HTML</title>
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<p>
</p>
<h1 class="title p-name" id="title" property="dcterms:title">Sourcing In-band Media Resource Tracks from Media Containers into HTML</h1>
<h2 property="dcterms:issued" datatype="xsd:dateTime" content="2014-06-05T18:04:11.000Z" id="unofficial-draft-06-june-2014">Unofficial Draft <time class="dt-published" datetime="2014-06-06">06 June 2014</time></h2>
<dl>
<dt>Latest editor's draft:</dt>
<dd><a href="http://rawgit.com/silviapfeiffer/HTMLSourcingInbandTracks/master/index.html">http://rawgit.com/silviapfeiffer/HTMLSourcingInbandTracks/master/index.html</a></dd>
<dt>Editors:</dt>
<dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><a class="u-url url p-name fn" rel="foaf:homepage" property="foaf:name" content="Silvia Pfeiffer" href="mailto:silviapfeiffer1@gmail.com">Silvia Pfeiffer</a>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://nicta.com.au/">NICTA</a></span>
</dd>
<dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><span property="foaf:name" class="p-name fn">Bob Lund</span>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://www.cablelabs.com/">CableLabs Inc</a></span>
</dd>
</dl>
<p class="copyright">
This document is licensed under a
<a class="subfoot" href="http://creativecommons.org/licenses/by/3.0/" rel="license">Creative Commons
Attribution 3.0 License</a>.
</p>
<hr>
</div>
<section id="abstract" class="introductory" property="dcterms:abstract" datatype="" typeof="bibo:Chapter" resource="#abstract" rel="bibo:Chapter"><h2 aria-level="1" role="heading" id="h2_abstract">Abstract</h2>
<p>
This specification is provided to promote interoperability among implementations and users of in-band text tracks sourced for [<cite><a class="bibref" href="#bib-HTML5">HTML5</a></cite>]/[<cite><a class="bibref" href="#bib-HTML">HTML</a></cite>] from media resource containers. The specification provides guidelines for the creation of video, audio and text tracks and their attribute values as mapped from in-band tracks from media resource types typically supported by User Agents. It also explains how the UA should map in-band text track content into text track cues.
</p>
<p>
Mappings are defined for [<cite><a class="bibref" href="#bib-MPEGDASH">MPEGDASH</a></cite>], [<cite><a class="bibref" href="#bib-ISOBMFF">ISOBMFF</a></cite>], [<cite><a class="bibref" href="#bib-MPEG2TS">MPEG2TS</a></cite>], [<cite><a class="bibref" href="#bib-OGGSKELETON">OGGSKELETON</a></cite>] and [<cite><a class="bibref" href="#bib-WebM">WebM</a></cite>].
</p>
</section><section id="sotd" class="introductory" typeof="bibo:Chapter" resource="#sotd" rel="bibo:Chapter"><h2 aria-level="1" role="heading" id="h2_sotd">Status of This Document</h2>
<p>
This document is merely a public working draft of a potential specification. It has
no official standing of any kind and does not represent the support or consensus of any
standards organisation.
</p>
<p>
This is the first draft. Please send feedback to: <a href="mailto:public-inbandtracks@w3.org">public-inbandtracks@w3.org</a>.
</p>
</section><section id="toc"><h2 class="introductory" aria-level="1" role="heading" id="h2_toc">Table of Contents</h2><ul class="toc" role="directory" id="respecContents"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a></li><li class="tocline"><a href="#mpegdash" class="tocxref"><span class="secno">2. </span>MPEG DASH</a></li><li class="tocline"><a href="#mpeg2ts" class="tocxref"><span class="secno">3. </span>MPEG-2 Transport Streams</a></li><li class="tocline"><a href="#mpeg4" class="tocxref"><span class="secno">4. </span>MPEG-4 ISOBMFF</a></li><li class="tocline"><a href="#webm" class="tocxref"><span class="secno">5. </span>WebM</a></li><li class="tocline"><a href="#ogg" class="tocxref"><span class="secno">6. </span>Ogg</a></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">A. </span>Acknowledgements</a></li></ul></section>
<section id="introduction">
<!--OddPage--><h2 aria-level="1" role="heading" id="h2_introduction"><span class="secno">1. </span>Introduction</h2>
<p>
The specification maintains mappings from in-band audio, video and other data tracks of MIME-type/subtype media resources to HTML VideoTrack, AudioTrack, and TextTrack objects and their attribute values.
</p>
<p>
A generic rule to follow is that a track as exposed in HTML only ever represents a single semantic concept. When mapping from a media resource, sometimes an in-band track does not relate 1-to-1 to a HTML text, audio or video track.
</p>
<div class="note"><div class="note-title" aria-level="2" role="heading" id="h_note_1"><span>Note</span></div><p class="">For example, a HTML TextTrack object is either a subtitle track or a caption track, never both. However, in-band text tracks may encapsulate caption and subtitle cues of the same language as a single in-band track. Since a caption track is essentially a subtitle track with additional cues of transcripts of audio-only information, such an encapsulation in a single in-band track can save space. In HTML, these tracks should be exposed as two TextTrack objects, since they represent different semantic concepts. The cues appear in their relevant tracks - subtitle cues would be present in both. This allows users to choose between the two tracks and activate the desired one in the same manner that they do when the two tracks are provided through two track elements.
</p></div>
<div class="note"><div class="note-title" aria-level="2" role="heading" id="h_note_2"><span>Note</span></div><p class="">
A similar logic applies to in-band text tracks that have subtitle cues of different languages mixed together in one track. They, too, should be exposed in a track of their own language each.
</p></div>
<div class="note"><div class="note-title" aria-level="2" role="heading" id="h_note_3"><span>Note</span></div><p class="">
A further example is when a UA decides to implement rendering for a caption track but without exposing the caption track through the TextTrack API. To the Web developer and the Web page user, such a video appears as though it has burnt-in captions. Therefore, the UA could expose two video tracks on the HTMLMediaElement - one with captions and a kind="captions" and one without captions with a kind="main". In this way, the user and the Web developer still get the choice of whether to see the video with or without captions.
</p></div>
<p>
Another generic rule to follow for in-band data tracks is that in order to map them to TextTrack objects, they need to be mapped to media-time aligned cues that relate to a non-zero interval of time.
</p>
<p>
For every MIME-type/subtype of an existing media container format, this specification defines the following information:
</p><ol>
<li>Track order.</li>
<li>How to identify the type of tracks.</li>
<li>Setting track attributes 'id', 'kind', 'language' and 'label' for sourced text tracks.</li>
<li>Setting track attributes 'id', 'kind', 'language' and 'label' for sourced audio and video tracks.</li>
<li>Mapping text track content into text track cues.</li>
</ol>
<p></p>
</section>
<section id="mpegdash" typeof="bibo:Chapter" resource="#mpegdash" rel="bibo:Chapter">
<!--OddPage--><h2 aria-level="1" role="heading" id="h2_mpegdash"><span class="secno">2. </span>MPEG DASH</h2>
<b>MIME type/subtype: application/dash+xml</b>
<ol>
<li>Track Order
<p>
The order of tracks specified in the MPD (Media Presentation Description) format [<cite><a class="bibref" href="#bib-MPEGDASH">MPEGDASH</a></cite>] is maintained when sourcing multiple MPEG DASH tracks into HTML.
</p>
</li>
<li>Determining the type of track
<p>
A user agent recognises and supports data from a MPEG DASH media resource as being equivalent to a HTML track based on the adaptationSet mimeType:
</p><ul>
<li>text track: the mimeType is of main type "application" or "text"</li>
<li>video track: the mimeType is of main type "video"</li>
<li>audio track: the mimeType is of main type "audio"</li>
</ul>
<p></p>
</li>
<li>Track Attributes for sourced Text Tracks
<p>
</p><table>
<thead>
<tr><th>Attribute</th>
<th>How to source its value</th>
</tr></thead>
<tbody><tr>
<th>id</th>
<td>
Content of the 'id' attribute in the AdaptationSet element. Empty string if 'id' attribute is not present.
</td>
</tr>
<tr>
<th>kind</th>
<td>
<p>Given URN="urn:mpeg:dash:role:2011":</p>
<ul>
<li>"captions": if the role descriptor's value is "caption"</li>
<li>"subtitles": if the role descriptor's value is "subtitle"</li>
<li>"metadata": otherwise</li>
</ul>
</td>
</tr>
<tr>
<th>label</th>
<td>
The empty string.
</td>
</tr>
<tr>
<th>language</th>
<td>
Content of the 'lang' attribute in the AdaptationSet element.
</td>
</tr>
</tbody></table>
<p></p>
</li>
<li>Track Attributes for sourced Audio and Video Tracks
<p>
</p><table>
<thead>
<tr><th>Attribute</th>
<th>How to source its value</th>
</tr></thead>
<tbody><tr>
<th>id</th>
<td>
Content of the 'id' attribute in the AdaptationSet element. Empty string if 'id' attribute is not present.
</td>
</tr>
<tr>
<th>kind</th>
<td>
<p>Given a role scheme of "urn:mpeg:dash:role:2011", determine the 'kind' attribute from the value of the role descriptors in the AdaptationSet element.</p>
<ul>
<li>"alternative": if the role is "alternate" but not also "main" or "commentary", or "dub"</li>
<li>"captions": if the role is "caption" and also "main"</li>
<li>"descriptions": if the role is "description" and also "supplementary"</li>
<li>"main": if the role is "main" but not also "caption", "subtitle", or "dub"</li>
<li>"main-desc": if the role is "main" and also "description"</li>
<li>"sign": not used</li>
<li>"subtitles": if the role is "subtitle" and also "main"</li>
<li>"translation": if the role is "dub" and also "main"</li>
<li>"commentary": if the role is "commentary" but not also "main"</li>
<li>"": otherwise</li>
</ul>
</td>
</tr>
<tr>
<th>label</th>
<td>
The empty string.
</td>
</tr>
<tr>
<th>language</th>
<td>
Content of the 'lang' attribute in the AdaptationSet element.
</td>
</tr>
</tbody></table>
<p></p>
</li>
<li>Mapping text track content into text track cues
<p>TBD</p>
</li>
</ol>
</section>
<section id="mpeg2ts" typeof="bibo:Chapter" resource="#mpeg2ts" rel="bibo:Chapter">
<!--OddPage--><h2 aria-level="1" role="heading" id="h2_mpeg2ts"><span class="secno">3. </span>MPEG-2 Transport Streams</h2>
<b>MIME type/subtype: audio/mp2t , video/mp2t</b>
<ol>
<li>Track Order
<p>
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Received on Friday, 6 June 2014 04:04:28 UTC