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<!DOCTYPE html>
<html lang="en" dir="ltr">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Media Source Extensions</title>
<style type="text/css">
.nonnormative { color: green; margin: 2em 0 2em 0em; padding: 0.5em 1em; border: none; background: #DDFFDD; }
.nonnormative h3 { color: inherit; background: inherit; }
.nonnormative:before { display: table; margin: -1em -0.5em -0.5em auto; width: auto; content: 'This section is non-normative.'; color: black; font-style: italic; border: solid 2px; background: white; padding: 0 0.25em; }
.iso-box { font-weight: bold; }
.iso-var { font-style: italic; }
table.old-table { border-collapse: collapse; border-style: hidden hidden none hidden; }
table.old-table thead, table tbody { border-bottom: solid; }
table.old-table tbody th:first-child { border-left: solid; }
table.old-table tbody th { text-align: left; }
table.old-table td, table th { border-left: solid; border-right: solid; border-bottom: solid thin; vertical-align: top; padding: 0.2em; }
dl.switch { padding-left: 2em; }
dl.switch > dt { text-indent: -1.5em; }
dl.switch > dt:before { content: '\21AA'; padding: 0 0.5em 0 0; display: inline-block; width: 1em; text-align: right; line-height: 0.5em; }
p + * > li, dd li { margin: 1em 0; }
@media screen { code :link, code :visited { color: inherit; } }
</style>
<style>/*****************************************************************
* ReSpec 3 CSS
* Robin Berjon - http://berjon.com/
*****************************************************************/
/* --- INLINES --- */
em.rfc2119 {
text-transform: lowercase;
font-variant: small-caps;
font-style: normal;
color: #900;
}
h1 acronym, h2 acronym, h3 acronym, h4 acronym, h5 acronym, h6 acronym, a acronym,
h1 abbr, h2 abbr, h3 abbr, h4 abbr, h5 abbr, h6 abbr, a abbr {
border: none;
}
dfn {
font-weight: bold;
}
a.internalDFN {
color: inherit;
border-bottom: 1px solid #99c;
text-decoration: none;
}
a.externalDFN {
color: inherit;
border-bottom: 1px dotted #ccc;
text-decoration: none;
}
a.bibref {
text-decoration: none;
}
cite .bibref {
font-style: normal;
}
code {
color: #ff4500;
}
/* --- --- */
ol.algorithm { counter-reset:numsection; list-style-type: none; }
ol.algorithm li { margin: 0.5em 0; }
ol.algorithm li:before { font-weight: bold; counter-increment: numsection; content: counters(numsection, ".") ") "; }
/* --- TOC --- */
.toc a, .tof a {
text-decoration: none;
}
a .secno, a .figno {
color: #000;
}
ul.tof, ol.tof {
list-style: none outside none;
}
.caption {
margin-top: 0.5em;
font-style: italic;
}
/* --- TABLE --- */
table.simple {
border-spacing: 0;
border-collapse: collapse;
border-bottom: 3px solid #005a9c;
}
.simple th {
background: #005a9c;
color: #fff;
padding: 3px 5px;
text-align: left;
}
.simple th[scope="row"] {
background: inherit;
color: inherit;
border-top: 1px solid #ddd;
}
.simple td {
padding: 3px 10px;
border-top: 1px solid #ddd;
}
.simple tr:nth-child(even) {
background: #f0f6ff;
}
/* --- DL --- */
.section dd > p:first-child {
margin-top: 0;
}
.section dd > p:last-child {
margin-bottom: 0;
}
.section dd {
margin-bottom: 1em;
}
.section dl.attrs dd, .section dl.eldef dd {
margin-bottom: 0;
}
</style><style>/* --- ISSUES/NOTES --- */
div.issue-title, div.note-title {
padding-right: 1em;
min-width: 7.5em;
color: #b9ab2d;
}
div.issue-title { color: #e05252; }
div.note-title { color: #52e052; }
div.issue-title span, div.note-title span {
text-transform: uppercase;
}
div.note, div.issue {
margin-top: 1em;
margin-bottom: 1em;
}
.note > p:first-child, .issue > p:first-child { margin-top: 0 }
.issue, .note {
padding: .5em;
border-left-width: .5em;
border-left-style: solid;
}
div.issue, div.note {
padding: 0.5em;
margin: 1em 0;
position: relative;
clear: both;
}
span.note, span.issue { padding: .1em .5em .15em; }
.issue {
border-color: #e05252;
background: #fbe9e9;
}
.note {
border-color: #52e052;
background: #e9fbe9;
}
</style><style>/* --- WEB IDL --- */
pre.idl {
border-top: 1px solid #90b8de;
border-bottom: 1px solid #90b8de;
padding: 1em;
line-height: 120%;
}
pre.idl::before {
content: "WebIDL";
display: block;
width: 150px;
background: #90b8de;
color: #fff;
font-family: initial;
padding: 3px;
font-weight: bold;
margin: -1em 0 1em -1em;
}
.idlType {
color: #ff4500;
font-weight: bold;
text-decoration: none;
}
/*.idlModule*/
/*.idlModuleID*/
/*.idlInterface*/
.idlInterfaceID, .idlDictionaryID, .idlCallbackID, .idlEnumID {
font-weight: bold;
color: #005a9c;
}
.idlSuperclass {
font-style: italic;
color: #005a9c;
}
/*.idlAttribute*/
.idlAttrType, .idlFieldType, .idlMemberType {
color: #005a9c;
}
.idlAttrName, .idlFieldName, .idlMemberName {
color: #ff4500;
}
.idlAttrName a, .idlFieldName a, .idlMemberName a {
color: #ff4500;
border-bottom: 1px dotted #ff4500;
text-decoration: none;
}
/*.idlMethod*/
.idlMethType, .idlCallbackType {
color: #005a9c;
}
.idlMethName {
color: #ff4500;
}
.idlMethName a {
color: #ff4500;
border-bottom: 1px dotted #ff4500;
text-decoration: none;
}
/*.idlParam*/
.idlParamType {
color: #005a9c;
}
.idlParamName {
font-style: italic;
}
.extAttr {
color: #666;
}
/*.idlConst*/
.idlConstType {
color: #005a9c;
}
.idlConstName {
color: #ff4500;
}
.idlConstName a {
color: #ff4500;
border-bottom: 1px dotted #ff4500;
text-decoration: none;
}
/*.idlException*/
.idlExceptionID {
font-weight: bold;
color: #c00;
}
.idlTypedefID, .idlTypedefType {
color: #005a9c;
}
.idlRaises, .idlRaises a.idlType, .idlRaises a.idlType code, .excName a, .excName a code {
color: #c00;
font-weight: normal;
}
.excName a {
font-family: monospace;
}
.idlRaises a.idlType, .excName a.idlType {
border-bottom: 1px dotted #c00;
}
.excGetSetTrue, .excGetSetFalse, .prmNullTrue, .prmNullFalse, .prmOptTrue, .prmOptFalse {
width: 45px;
text-align: center;
}
.excGetSetTrue, .prmNullTrue, .prmOptTrue { color: #0c0; }
.excGetSetFalse, .prmNullFalse, .prmOptFalse { color: #c00; }
.idlImplements a {
font-weight: bold;
}
dl.attributes, dl.methods, dl.constants, dl.fields, dl.dictionary-members {
margin-left: 2em;
}
.attributes dt, .methods dt, .constants dt, .fields dt, .dictionary-members dt {
font-weight: normal;
}
.attributes dt code, .methods dt code, .constants dt code, .fields dt code, .dictionary-members dt code {
font-weight: bold;
color: #000;
font-family: monospace;
}
.attributes dt code, .fields dt code, .dictionary-members dt code {
background: #ffffd2;
}
.attributes dt .idlAttrType code, .fields dt .idlFieldType code, .dictionary-members dt .idlMemberType code {
color: #005a9c;
background: transparent;
font-family: inherit;
font-weight: normal;
font-style: italic;
}
.methods dt code {
background: #d9e6f8;
}
.constants dt code {
background: #ddffd2;
}
.attributes dd, .methods dd, .constants dd, .fields dd, .dictionary-members dd {
margin-bottom: 1em;
}
table.parameters, table.exceptions {
border-spacing: 0;
border-collapse: collapse;
margin: 0.5em 0;
width: 100%;
}
table.parameters { border-bottom: 1px solid #90b8de; }
table.exceptions { border-bottom: 1px solid #deb890; }
.parameters th, .exceptions th {
color: #fff;
padding: 3px 5px;
text-align: left;
font-family: initial;
font-weight: normal;
text-shadow: #666 1px 1px 0;
}
.parameters th { background: #90b8de; }
.exceptions th { background: #deb890; }
.parameters td, .exceptions td {
padding: 3px 10px;
border-top: 1px solid #ddd;
vertical-align: top;
}
.parameters tr:first-child td, .exceptions tr:first-child td {
border-top: none;
}
.parameters td.prmName, .exceptions td.excName, .exceptions td.excCodeName {
width: 100px;
}
.parameters td.prmType {
width: 120px;
}
table.exceptions table {
border-spacing: 0;
border-collapse: collapse;
width: 100%;
}
</style><link rel="stylesheet" href="//www.w3.org/StyleSheets/TR/W3C-WD"><!--[if lt IE 9]><script src='http://www.w3.org/2008/site/js/html5shiv.js'></script><![endif]--></head>
<body><div class="head">
<p>
<a href="http://www.w3.org/"><img width="72" height="48" src="http://www.w3.org/Icons/w3c_home" alt="W3C"></a>
</p>
<h1 class="title" id="title">Media Source Extensions</h1>
<h2 id="w3c-working-draft-24-january-2013"><abbr title="World Wide Web Consortium">W3C</abbr> Working Draft 24 January 2013</h2>
<dl>
<dt>This version:</dt>
<dd><a href="http://www.w3.org/TR/2013/WD-media-source-20130124/">http://www.w3.org/TR/2013/WD-media-source-20130124/</a></dd>
<dt>Latest published version:</dt>
<dd><a href="http://www.w3.org/TR/media-source/">http://www.w3.org/TR/media-source/</a></dd>
<dt>Latest editor's draft:</dt>
<dd><a href="http://dvcs.w3.org/hg/html-media/raw-file/tip/media-source/media-source.html">http://dvcs.w3.org/hg/html-media/raw-file/tip/media-source/media-source.html</a></dd>
<dt>Editors:</dt>
<dd><span>Aaron Colwell</span>, <a href="http://www.google.com/">Google Inc.</a></dd>
<dd><span>Adrian Bateman</span>, <a href="http://www.microsoft.com/">Microsoft Corporation</a></dd>
<dd><span>Mark Watson</span>, <a href="http://www.netflix.com/">Netflix Inc.</a></dd>
</dl>
<p class="copyright">
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> ©
2013
<a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup>
(<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>,
<a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved.
<abbr title="World Wide Web Consortium">W3C</abbr> <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and
<a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules apply.
</p>
<hr>
</div>
<section id="abstract" class="introductory"><h2>Abstract</h2><p>
This specification extends HTMLMediaElement to allow
JavaScript to generate media streams for playback.
Allowing JavaScript to generate streams facilitates a variety of use
cases like adaptive streaming and time shifting live streams.
</p></section><section id="sotd" class="introductory"><h2>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="http://www.w3.org/TR/"><abbr title="World Wide Web Consortium">W3C</abbr> technical reports
index</a> at http://www.w3.org/TR/.</em>
</p>
<p>The working groups maintains <a href="http://w3.org/brief/Mjcw">a list of all bug reports that the editors have not yet tried to address</a>. 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.</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="http://www.w3.org/html/wg/">HTML Working Group</a> as a First Public Working Draft.
This document is intended to become a <abbr title="World Wide Web Consortium">W3C</abbr> Recommendation.
If you wish to make comments regarding this document, 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="http://lists.w3.org/Archives/Public/public-html-media/">archives</a>).
All feedback is welcome.
</p>
<p>
Publication as a Working 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="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 <abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>.
<abbr title="World Wide Web Consortium">W3C</abbr> maintains a <a href="http://www.w3.org/2004/01/pp-impl/40318/status" rel="disclosure">public list of any patent disclosures</a>
made in connection with the deliverables of the group; that page also includes instructions for
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</section><section id="toc"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#goals" class="tocxref"><span class="secno">1.1 </span>Goals</a></li><li class="tocline"><a href="#definitions" class="tocxref"><span class="secno">1.2 </span>Definitions</a></li></ul></li><li class="tocline"><a href="#source-buffer-model" class="tocxref"><span class="secno">2. </span>Source Buffer Model</a><ul class="toc"><li class="tocline"><a href="#source-buffer-overlapping-segments" class="tocxref"><span class="secno">2.1 </span>Appending a Media Segment over a buffered region</a><ul class="toc"><li class="tocline"><a href="#source-buffer-overlap-complete" class="tocxref"><span class="secno">2.1.1 </span>Complete Overlap</a></li><li class="tocline"><a href="#source-buffer-overlap-start" class="tocxref"><span class="secno">2.1.2 </span>Start Overlap</a></li><li class="tocline"><a href="#source-buffer-overlap-end" class="tocxref"><span class="secno">2.1.3 </span>End Overlap</a></li><li class="tocline"><a href="#source-buffer-overlap-middle" class="tocxref"><span class="secno">2.1.4 </span>Middle Overlap</a></li></ul></li><li class="tocline"><a href="#track-buffer-to-decoder-buffer" class="tocxref"><span class="secno">2.2 </span>Track Buffer to Decoder Buffer transfer</a></li></ul></li><li class="tocline"><a href="#mediasource" class="tocxref"><span class="secno">3. </span>MediaSource Object</a><ul class="toc"><li class="tocline"><a href="#attributes" class="tocxref"><span class="secno">3.1 </span>Attributes</a></li><li class="tocline"><a href="#methods" class="tocxref"><span class="secno">3.2 </span>Methods</a></li><li class="tocline"><a href="#mediasource-events" class="tocxref"><span class="secno">3.3 </span>Event Summary</a></li><li class="tocline"><a href="#mediasource-algorithms" class="tocxref"><span class="secno">3.4 </span>Algorithms</a><ul class="toc"><li class="tocline"><a href="#mediasource-attach" class="tocxref"><span class="secno">3.4.1 </span>Attaching to a media element</a></li><li class="tocline"><a href="#mediasource-detach" class="tocxref"><span class="secno">3.4.2 </span>Detaching from a media element</a></li><li class="tocline"><a href="#mediasource-seeking" class="tocxref"><span class="secno">3.4.3 </span>Seeking</a></li><li class="tocline"><a href="#buffer-monitoring" class="tocxref"><span class="secno">3.4.4 </span>SourceBuffer Monitoring</a></li><li class="tocline"><a href="#active-source-buffer-changes" class="tocxref"><span class="secno">3.4.5 </span>Changes to selected/enabled track state</a></li><li class="tocline"><a href="#duration-change-algorithm" class="tocxref"><span class="secno">3.4.6 </span>Duration change</a></li></ul></li></ul></li><li class="tocline"><a href="#sourcebuffer" class="tocxref"><span class="secno">4. </span>SourceBuffer Object</a><ul class="toc"><li class="tocline"><a href="#attributes-1" class="tocxref"><span class="secno">4.1 </span>Attributes</a></li><li class="tocline"><a href="#methods-1" class="tocxref"><span class="secno">4.2 </span>Methods</a></li><li class="tocline"><a href="#track-buffers" class="tocxref"><span class="secno">4.3 </span>Track Buffers</a></li><li class="tocline"><a href="#sourcebuffer-events" class="tocxref"><span class="secno">4.4 </span>Event Summary</a></li><li class="tocline"><a href="#sourcebuffer-algorithms" class="tocxref"><span class="secno">4.5 </span>Algorithms</a><ul class="toc"><li class="tocline"><a href="#sourcebuffer-segment-parser-loop" class="tocxref"><span class="secno">4.5.1 </span>Segment Parser Loop</a></li><li class="tocline"><a href="#sourcebuffer-reset-parser-state" class="tocxref"><span class="secno">4.5.2 </span>Reset Parser State</a></li><li class="tocline"><a href="#sourcebuffer-append-error" class="tocxref"><span class="secno">4.5.3 </span>Append Error</a></li><li class="tocline"><a href="#sourcebuffer-stream-append-loop" class="tocxref"><span class="secno">4.5.4 </span>Stream Append Loop</a></li><li class="tocline"><a href="#sourcebuffer-init-segment-received" class="tocxref"><span class="secno">4.5.5 </span>Initialization Segment Received</a></li><li class="tocline"><a href="#sourcebuffer-coded-frame-processing" class="tocxref"><span class="secno">4.5.6 </span>Coded Frame Processing</a></li></ul></li></ul></li><li class="tocline"><a href="#sourcebufferlist" class="tocxref"><span class="secno">5. </span>SourceBufferList Object</a><ul class="toc"><li class="tocline"><a href="#attributes-2" class="tocxref"><span class="secno">5.1 </span>Attributes</a></li><li class="tocline"><a href="#methods-2" class="tocxref"><span class="secno">5.2 </span>Methods</a></li><li class="tocline"><a href="#sourcebufferlist-events" class="tocxref"><span class="secno">5.3 </span>Event Summary</a></li></ul></li><li class="tocline"><a href="#url" class="tocxref"><span class="secno">6. </span>URL Object</a><ul class="toc"><li class="tocline"><a href="#methods-3" class="tocxref"><span class="secno">6.1 </span>Methods</a></li></ul></li><li class="tocline"><a href="#htmlmediaelement-attributes" class="tocxref"><span class="secno">7. </span>HTMLMediaElement attributes</a></li><li class="tocline"><a href="#byte-stream-formats" class="tocxref"><span class="secno">8. </span>Byte Stream Formats</a><ul class="toc"><li class="tocline"><a href="#webm" class="tocxref"><span class="secno">8.1 </span>WebM Byte Streams</a><ul class="toc"><li class="tocline"><a href="#webm-init-segments" class="tocxref"><span class="secno">8.1.1 </span>Initialization Segments</a></li><li class="tocline"><a href="#webm-media-segments" class="tocxref"><span class="secno">8.1.2 </span>Media Segments</a></li><li class="tocline"><a href="#webm-random-access-points" class="tocxref"><span class="secno">8.1.3 </span>Random Access Points</a></li></ul></li><li class="tocline"><a href="#iso" class="tocxref"><span class="secno">8.2 </span>ISO Base Media File Format Byte Streams</a><ul class="toc"><li class="tocline"><a href="#iso-init-segments" class="tocxref"><span class="secno">8.2.1 </span>Initialization Segments</a></li><li class="tocline"><a href="#iso-media-segments" class="tocxref"><span class="secno">8.2.2 </span>Media Segments</a></li><li class="tocline"><a href="#iso-random-access-points" class="tocxref"><span class="secno">8.2.3 </span>Random Access Points</a></li></ul></li><li class="tocline"><a href="#mpeg2ts" class="tocxref"><span class="secno">8.3 </span>MPEG-2 Transport Stream Byte Streams</a><ul class="toc"><li class="tocline"><a href="#mpeg2ts-general" class="tocxref"><span class="secno">8.3.1 </span>General</a></li><li class="tocline"><a href="#mpeg2ts-init-segments" class="tocxref"><span class="secno">8.3.2 </span>Initialization Segments</a></li><li class="tocline"><a href="#mpeg2ts-media-segments" class="tocxref"><span class="secno">8.3.3 </span>Media Segments</a></li><li class="tocline"><a href="#mpeg2ts-random-access-points" class="tocxref"><span class="secno">8.3.4 </span>Random Access Points</a></li><li class="tocline"><a href="#mpeg2ts-discontinuities" class="tocxref"><span class="secno">8.3.5 </span>Timestamp Rollover & Discontinuities</a></li></ul></li></ul></li><li class="tocline"><a href="#examples" class="tocxref"><span class="secno">9. </span>Examples</a></li><li class="tocline"><a href="#revision-history" class="tocxref"><span class="secno">10. </span>Revision History</a></li></ul></section>
<section id="introduction">
<!--OddPage--><h2><span class="secno">1. </span>Introduction</h2>
<p>This specification allows JavaScript to dynamically construct media streams for <audio> and <video>.
It defines objects that allow JavaScript to pass media segments to an <a href="http://www.w3.org/TR/html5/embedded-content-0.html#htmlmediaelement">HTMLMediaElement</a>.
A buffering model is also included to describe how the user agent should act when different media segments are
appended at different times. Byte stream specifications for WebM, ISO Base Media File Format, and MPEG-2 Transport Streams are given to specify the
expected format of byte streams used with these extensions.</p>
<img src="pipeline_model.png" alt="Media Source Pipeline Model Diagram">
<section id="goals">
<h3><span class="secno">1.1 </span>Goals</h3>
<p>This specification was designed with the following goals in mind:</p>
<ul>
<li>Allow JavaScript to construct media streams independent of how the media is fetched.</li>
<li>Define a splicing and buffering model that facilitates use cases like adaptive streaming, ad-insertion, time-shifting, and video editing.</li>
<li>Minimize the need for media parsing in JavaScript.</li>
<li>Leverage the browser cache as much as possible.</li>
<li>Provide byte stream definitions for WebM, the ISO Base Media File Format, and MPEG-2 Transport Streams.</li>
<li>Not require support for any particular media format or codec.</li>
</ul>
</section>
<section id="definitions">
<h3><span class="secno">1.2 </span>Definitions</h3>
<dl>
<dt id="init-segment">Initialization Segment</dt>
<dd>
<p>A sequence of bytes that contain all of the initialization information required to decode a sequence of <a href="#media-segment">media segments</a>. This includes codec initialization data, <a href="#track-id">Track ID</a> mappings for multiplexed segments, and timestamp offsets (e.g. edit lists).</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">The <a href="#byte-stream-formats">byte stream format specifications</a> contain format specific examples.</p></div>
</dd><dt id="media-segment">Media Segment</dt>
<dd>
<p>A sequence of bytes that contain packetized & timestamped media data for a portion of the presentation timeline. Media segments are always associated with the most recently appended <a href="#init-segment">initialization segment</a>.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">The <a href="#byte-stream-formats">byte stream format specifications</a> contain format specific examples.</p></div>
</dd>
<dt id="decoder-buffer">Decoder Buffer</dt>
<dd><p>A buffer that holds initialization data and <a href="#coded-frame">coded frames</a> that will be decoded and rendered. This buffer may not exist in actual implementations, but it is intended to represent media data that will be decoded no matter what <a href="#media-segment">media segments</a> are appended to update the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a>. This distinction is important when considering appends that happen close to the current playback position. See <a href="#track-buffer-to-decoder-buffer">Track Buffer to Decoder Buffer transfer</a> for details.</p></dd>
<dt id="random-access-point">Random Access Point</dt>
<dd><p>A position in a <a href="#media-segment">media segment</a> where decoding and continuous playback can begin without relying on any previous data in the segment. For video this tends to be the location of I-frames. In the case of audio, most audio frames can be treated as a random access point. Since video tracks tend to have a more sparse distribution of random access points, the location of these points are usually considered the random access points for multiplexed streams.</p></dd>
<dt id="presentation-start-time">Presentation Start Time</dt>
<dd><p>The presentation start time is the earliest time point in the presentation and specifies the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#initial-playback-position">initial playback position</a> and <a href="http://www.w3.org/TR/html5/embedded-content-0.html#earliest-possible-position">earliest possible position</a>. All presentations created using this specification have a presentation start time of 0.</p></dd>
<dt id="mediasource-object-url">MediaSource object URL</dt>
<dd>
<p>A MediaSource object URL is a unique <a href="http://www.w3.org/TR/FileAPI/#url">Blob URI</a> created by <code><a href="#widl-URL-createObjectURL-DOMString-MediaSource-mediaSource">createObjectURL()</a></code>. It is used to attach a <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> object to an HTMLMediaElement.</p>
<p>These URLs are the same as what the <a href="http://www.w3.org/TR/FileAPI/#">File API</a> specification calls a <a href="http://www.w3.org/TR/FileAPI/#url">Blob URI</a>, except that anything in the definition of that feature that refers to <a href="http://www.w3.org/TR/FileAPI/#dfn-file">File</a> and <a href="http://www.w3.org/TR/FileAPI/#dfn-Blob">Blob</a> objects is hereby extended to also apply to <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> objects.</p>
</dd>
<dt id="track-id">Track ID</dt>
<dd><p>A Track ID is a byte stream format specific identifier that marks sections of the byte stream as being part of a specific track. The Track ID in a <a href="#track-description">track description</a> identifies which sections of a <a href="#media-segment">media segment</a> belong to that track.</p></dd>
<dt id="track-description">Track Description</dt>
<dd><p>A byte stream format specific structure that provides the <a href="#track-id">Track ID</a>, codec configuration, and other metadata for a single track. Each track description inside a single <a href="#init-segment">initialization segment</a> must have a unique <a href="#track-id">Track ID</a>.</p></dd>
<dt id="coded-frame">Coded Frame</dt>
<dd><p>A unit of compressed media data that has a presentation timestamp and decode timestamp. The presentation timestamp indicates when the frame should be rendered. The decode timestamp indicates when the frame needs to be decoded. If frames can be decoded out of order, then the decode timestamp must be present in the bytestream. If frames cannot be decoded out of order and a decode timestamp is not present in the bytestream, then the decode timestamp is equal to the presentation timestamp.</p></dd>
<dt id="parent-media-source">Parent Media Source</dt>
<dd>The parent media source of a <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object is the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> object that created it.</dd>
<dt id="append-sequence">Append Sequence</dt>
<dd>A series of <code><a href="#widl-SourceBuffer-appendArrayBuffer-void-ArrayBuffer-data">appendArrayBuffer()</a></code> or <code><a href="#widl-SourceBuffer-appendStream-void-Stream-stream-unsigned-long-long-maxSize">appendStream()</a></code> calls on a <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> without any intervening <code><a href="#widl-SourceBuffer-abort-void">abort()</a></code> calls. The
<a href="#media-segment">media segments</a> in an append sequence must be adjacent and monotonically increasing in time without any gaps. An
<code><a href="#widl-SourceBuffer-abort-void">abort()</a></code> call starts a new append sequence which allows <a href="#media-segment">media segments</a> to be appended in non-monotonically
increasing order.</dd>
</dl>
</section>
</section>
<section id="source-buffer-model">
<!--OddPage--><h2><span class="secno">2. </span>Source Buffer Model</h2>
<div class="nonnormative">
<p>The subsections below outline the buffering model for this specification. It describes the various rules and behaviors associated with appending
data to an individual <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a>. At the highest level, the web application creates <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects and appends sequences of
<a href="#init-segment">initialization segments</a> and <a href="#media-segment">media segments</a> to update their state. The media element pulls media data out of the
<a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> object, plays it, and fires events just like it would if a normal URL was passed to the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#attr-media-src">src</a></code> attribute.
The web application is expected to monitor media element events to determine when it needs to append more <a href="#media-segment">media segments</a>.</p>
</div>
<section id="source-buffer-overlapping-segments">
<h3><span class="secno">2.1 </span>Appending a Media Segment over a buffered region</h3>
<p>There are several ways that <a href="#media-segment">media segments</a> can overlap segments in the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a>. Behavior for the different overlap situations are described below. If more than one overlap applies, then the <a href="#source-buffer-overlap-start">start overlap</a> must be resolved first, followed by any <a href="#source-buffer-overlap-complete">complete overlaps</a>, and finally the <a href="#source-buffer-overlap-end">end overlap</a>. If a segment contains multiple tracks then the overlap is resolved independently for each track.</p>
<div class="issue"><div class="issue-title"><span>Issue 1</span></div><p class=""><a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=19673">Bug 19673</a> - Seamless audio signal transitions at splice points</p></div>
<div class="issue"><div class="issue-title"><span>Issue 2</span></div><p class=""><a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=19784">Bug 19784</a> - timestampOffset with multiplexed Media Segments</p></div>
<section id="source-buffer-overlap-complete">
<h4><span class="secno">2.1.1 </span>Complete Overlap</h4>
<img src="https://dvcs.w3.org/hg/html-media/raw-file/0e5e12a7750f/media-source/complete_overlap.png" alt="Complete overlap diagram">
<p>The figure above shows how the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> is updated when a new <a href="#media-segment">media segment</a> completely overlaps a segment in the buffer. In this case, the new segment completely replaces the old segment.</p>
</section>
<section id="source-buffer-overlap-start">
<h4><span class="secno">2.1.2 </span>Start Overlap</h4>
<img src="https://dvcs.w3.org/hg/html-media/raw-file/0e5e12a7750f/media-source/start_overlap.png" alt="Start overlap diagram">
<p>The figure above shows how the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> is updated when the beginning of a new <a href="#media-segment">media segment</a> overlaps a segment in the buffer. In this case, the new segment replaces all the old media data in the overlapping region. Since <a href="#media-segment">media segments</a> are constrained to starting with <a href="#random-access-point">random access points</a>, this provides a seamless transition between segments.</p>
<p>When an audio frame in the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> overlaps with the start of the new <a href="#media-segment">media segment</a> special behavior is required. At a minimum implementations must support dropping the old audio frame that overlaps the start of the new segment and insert silence for the small gap that is created. Higher quality implementations may support crossfading or crosslapping between the overlapping audio frames. No matter which strategy is implemented, no gaps are created in the ranges reported by <code><a href="#widl-SourceBuffer-buffered">buffered</a></code> and playback must never stall at the overlap.</p>
</section>
<section id="source-buffer-overlap-end">
<h4><span class="secno">2.1.3 </span>End Overlap</h4>
<img src="https://dvcs.w3.org/hg/html-media/raw-file/0e5e12a7750f/media-source/end_overlap.png" alt="End overlap diagram">
<p>The figure above shows how the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> is updated when the end of a new <a href="#media-segment">media segment</a> overlaps the beginning of a segment in the buffer. In this case, the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> tries to keep as much of the old segment as possible. The amount saved depends on where the closest <a href="#random-access-point">random access point</a>, in the old segment, is to the end of the new segment. In the case of audio, if the gap is smaller than the size of an audio frame, then the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> may render silence for this gap. This gap must not be reflect in <code><a href="#widl-SourceBuffer-buffered">buffered</a></code>. The entire new segment must be added to the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a>, but it is up to the implementation to determine how much of the old segment data is retained.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">An implementation may keep old segment data before the end of the new segment to avoid creating a gap if it wishes. Doing this though can significantly increase implementation complexity and could cause delays at the splice point.</p></div>
<div class="note"><div class="note-title"><span>Note</span></div><p class=""> The web application can use <code><a href="#widl-SourceBuffer-buffered">buffered</a></code> to determine how much of the old segment was preserved.</p></div>
</section>
<section id="source-buffer-overlap-middle">
<h4><span class="secno">2.1.4 </span>Middle Overlap</h4>
<img src="https://dvcs.w3.org/hg/html-media/raw-file/0e5e12a7750f/media-source/middle_overlap.png" alt="Middle overlap diagram">
<p>The figure above shows how the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> is updated when the new <a href="#media-segment">media segment</a> is in the middle of the old segment. This condition is handled by first resolving the <a href="#source-buffer-overlap-start">start overlap</a> and then resolving the <a href="#source-buffer-overlap-end">end overlap</a>.</p>
</section>
</section>
<section id="track-buffer-to-decoder-buffer">
<h3><span class="secno">2.2 </span>Track Buffer to Decoder Buffer transfer</h3>
<div class="nonnormative">
<p>The <a href="#track-buffer">track buffer</a> represents the media that the web application would like the media element to play. The <a href="#decoder-buffer">decoder buffer</a> contains the data that will actually get decoded and rendered. In most cases the <a href="#decoder-buffer">decoder buffer</a> will simply contain a subset of the <a href="#track-buffer">track buffer</a> near the current playback position. These two buffers start to diverge when <a href="#media-segment">media segments</a> that overlap or are very close to the current playback position are appended. Depending on the contents of the new <a href="#media-segment">media segment</a> it may not be possible to switch to the new data immediately because there isn't a <a href="#random-access-point">random access point</a> close enough to the current playback position. The quality of the implementation determines how much data is considered "in the <a href="#decoder-buffer">decoder buffer</a>." It should transfer data to the <a href="#decoder-buffer">decoder buffer</a> as late as possible whilst maintaining seamless playback. Some implementations may be able to instantiate multiple decoders or decode the new data significantly faster than real-time to achieve a seamless splice immediately. Other implementations may delay until the next <a href="#random-access-point">random access point</a> before switching to the newly appended data. Notice that this difference in behavior is only observable when appending close to the current playback position. The <a href="#decoder-buffer">decoder buffer</a> represents a media subsegment, like a group of pictures or something with similar decode dependencies, that the media element commits to playing. This commitment may be influenced by a variety of things like limited decoding resources, hardware decode buffers, a jitter buffer, or the desire to limit implementation complexity.</p>
<p>Here is an example to help clarify the role of the <a href="#decoder-buffer">decoder buffer</a>. Say the current playback position has a timestamp of 8 and the media element pulled frames with timestamp 9 & 10 into the decoder buffer. The web application then appends a higher quality <a href="#media-segment">media segment</a> that starts with a <a href="#random-access-point">random access point</a> at timestamp 9. The <a href="#track-buffer">track buffer</a> will get updated with the higher quality data, but the media element won't be able to switch to this higher quality data until the next <a href="#random-access-point">random access point</a> at timestamp 20. This is because a frame for timestamp 9 is already in the decoder buffer. The decoder buffer represents the "point of no return." for decoding. If a seek occurs the media element may choose to use the higher quality data since a seek might imply flushing the <a href="#decoder-buffer">decoder buffer</a> and the user expects a break in playback.</p>
</div>
</section>
</section>
<section id="mediasource">
<!--OddPage--><h2><span class="secno">3. </span>MediaSource Object</h2>
<p>The MediaSource object represents a source of media data for an HTMLMediaElement. It keeps track of the <code><a href="#widl-MediaSource-readyState">readyState</a></code> for this source as well as a list of <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects that can be used to add media data to the presentation. MediaSource objects are created by the web application and then attached to an HTMLMediaElement. The application uses the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> to add media data to this source. The HTMLMediaElement fetches this media data from the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> object when it is needed during playback.</p>
<pre class="idl"><span class="idlEnum" id="idl-def-ReadyState">enum <span class="idlEnumID">ReadyState</span> {
"<span class="idlEnumItem">closed</span>",
"<span class="idlEnumItem">open</span>",
"<span class="idlEnumItem">ended</span>"
};</span></pre><table class="simple"><tr><th colspan="2">Enumeration description</th></tr><tr><td><code>closed</code></td><td>
Indicates the source is not currently attached to a media element.
</td></tr><tr><td><code>open</code></td><td>
The source has been opened by a media element and is ready for data to be appended to the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>.
</td></tr><tr><td><code>ended</code></td><td>
The source is still attached to a media element, but <code><a href="#widl-MediaSource-endOfStream-void-EndOfStreamError-error">endOfStream()</a></code> has been called.
</td></tr></table>
<pre class="idl"><span class="idlEnum" id="idl-def-EndOfStreamError">enum <span class="idlEnumID">EndOfStreamError</span> {
"<span class="idlEnumItem">network</span>",
"<span class="idlEnumItem">decode</span>"
};</span></pre><table class="simple"><tr><th colspan="2">Enumeration description</th></tr><tr><td><code>network</code></td><td>
<p>Terminates playback and signals that a network error has occured.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">If the JavaScript fetching media data encounters a network error it should use this status code to terminate playback.</p></div>
</td></tr><tr><td><code>decode</code></td><td>
<p>Terminates playback and signals that a decoding error has occured.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">If the JavaScript code fetching media data has problems parsing the data it should use this status code to terminate playback.</p></div>
</td></tr></table>
<pre class="idl"><span class="idlInterface" id="idl-def-MediaSource">[<span class="extAttr">Constructor</span>]
interface <span class="idlInterfaceID">MediaSource</span> : <span class="idlSuperclass"><a>EventTarget</a></span> {
<span class="idlAttribute"> readonly attribute <span class="idlAttrType"><a href="#idl-def-SourceBufferList" class="idlType"><code>SourceBufferList</code></a></span> <span class="idlAttrName"><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></span>;</span>
<span class="idlAttribute"> readonly attribute <span class="idlAttrType"><a href="#idl-def-SourceBufferList" class="idlType"><code>SourceBufferList</code></a></span> <span class="idlAttrName"><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></span>;</span>
<span class="idlAttribute"> readonly attribute <span class="idlAttrType"><a href="#idl-def-ReadyState" class="idlType"><code>ReadyState</code></a></span> <span class="idlAttrName"><a href="#widl-MediaSource-readyState">readyState</a></span>;</span>
<span class="idlAttribute"> attribute <span class="idlAttrType"><a>unrestricted double</a></span> <span class="idlAttrName"><a href="#widl-MediaSource-duration">duration</a></span>;</span>
<span class="idlMethod"> <span class="idlMethType"><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a></span> <span class="idlMethName"><a href="#widl-MediaSource-addSourceBuffer-SourceBuffer-DOMString-type">addSourceBuffer</a></span> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">type</span></span>);</span>
<span class="idlMethod"> <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-MediaSource-removeSourceBuffer-void-SourceBuffer-sourceBuffer">removeSourceBuffer</a></span> (<span class="idlParam"><span class="idlParamType"><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a></span> <span class="idlParamName">sourceBuffer</span></span>);</span>
<span class="idlMethod"> <span class="idlMethType"><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a>?</span> <span class="idlMethName"><a href="#widl-MediaSource-getSourceBuffer-SourceBuffer-VideoTrack-videoTrack">getSourceBuffer</a></span> (<span class="idlParam"><span class="idlParamType"><a>VideoTrack</a></span> <span class="idlParamName">videoTrack</span></span>);</span>
<span class="idlMethod"> <span class="idlMethType"><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a>?</span> <span class="idlMethName"><a href="#widl-MediaSource-getSourceBuffer-SourceBuffer-AudioTrack-audioTrack">getSourceBuffer</a></span> (<span class="idlParam"><span class="idlParamType"><a>AudioTrack</a></span> <span class="idlParamName">audioTrack</span></span>);</span>
<span class="idlMethod"> <span class="idlMethType"><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a>?</span> <span class="idlMethName"><a href="#widl-MediaSource-getSourceBuffer-SourceBuffer-TextTrack-textTrack">getSourceBuffer</a></span> (<span class="idlParam"><span class="idlParamType"><a>TextTrack</a></span> <span class="idlParamName">textTrack</span></span>);</span>
<span class="idlMethod"> <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-MediaSource-endOfStream-void-EndOfStreamError-error">endOfStream</a></span> (<span class="idlParam">optional <span class="idlParamType"><a href="#idl-def-EndOfStreamError" class="idlType"><code>EndOfStreamError</code></a></span> <span class="idlParamName">error</span></span>);</span>
<span class="idlMethod"> <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-MediaSource-setTrackInfo-void-VideoTrack-track-DOMString-kind-DOMString-language">setTrackInfo</a></span> (<span class="idlParam"><span class="idlParamType"><a>VideoTrack</a></span> <span class="idlParamName">track</span></span>, <span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">kind</span></span>, <span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">language</span></span>);</span>
<span class="idlMethod"> <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-MediaSource-setTrackInfo-void-AudioTrack-track-DOMString-kind-DOMString-language">setTrackInfo</a></span> (<span class="idlParam"><span class="idlParamType"><a>AudioTrack</a></span> <span class="idlParamName">track</span></span>, <span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">kind</span></span>, <span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">language</span></span>);</span>
<span class="idlMethod"> <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-MediaSource-setTrackInfo-void-TextTrack-track-DOMString-kind-DOMString-language">setTrackInfo</a></span> (<span class="idlParam"><span class="idlParamType"><a>TextTrack</a></span> <span class="idlParamName">track</span></span>, <span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">kind</span></span>, <span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">language</span></span>);</span>
<span class="idlMethod"> static <span class="idlMethType"><a>bool</a></span> <span class="idlMethName"><a href="#widl-MediaSource-isTypeSupported-bool-DOMString-type">isTypeSupported</a></span> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">type</span></span>);</span>
};</span></pre><section id="attributes"><h3><span class="secno">3.1 </span>Attributes</h3><dl class="attributes"><dt id="widl-MediaSource-activeSourceBuffers"><code>activeSourceBuffers</code> of type <span class="idlAttrType"><a href="#idl-def-SourceBufferList" class="idlType"><code>SourceBufferList</code></a></span>, readonly</dt><dd>
<p>Contains the subset of <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> that are providing the
<a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-videotrack-selected">selected video track</a>, the
<a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-audiotrack-enabled">enabled audio tracks</a>, and the
<a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-texttrack-showing">"showing"</a> or <a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-texttrack-hidden">"hidden"</a> text tracks.
</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">The <a href="#active-source-buffer-changes">Changes to selected/enabled track state</a> section describes how this attribute gets
updated.</p></div>
</dd><dt id="widl-MediaSource-duration"><code>duration</code> of type <span class="idlAttrType"><a>unrestricted double</a></span></dt><dd>
<p>Allows the web application to set the presentation duration. The duration is initially set to NaN when the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> object is created.</p>
<p>On getting, run the following steps:</p>
<ol>
<li>If the <code><a href="#widl-MediaSource-readyState">readyState</a></code> attribute is <code><a href="#idl-def-ReadyState">"closed"</a></code> then return NaN and abort these steps.</li>
<li>Return the current value of the attribute.</li>
</ol>
<p>On setting, run the following steps:</p>
<ol>
<li>If the value being set is negative or NaN then throw an <code><a href="http://dom.spec.whatwg.org/#dom-domexception-invalid_access_err">INVALID_ACCESS_ERR</a></code> exception and abort these steps.</li>
<li>If the <code><a href="#widl-MediaSource-readyState">readyState</a></code> attribute is not <code><a href="#idl-def-ReadyState">"open"</a></code> then throw an <code><a href="http://dom.spec.whatwg.org/#dom-domexception-invalid_state_err">INVALID_STATE_ERR</a></code> exception and abort these steps.</li>
<li>Run the <a href="#duration-change-algorithm">duration change algorithm</a> with <var>new duration</var> set to the value being assigned to this attribute.
<div class="note"><div class="note-title"><span>Note</span></div><p class=""><code><a href="#widl-SourceBuffer-appendArrayBuffer-void-ArrayBuffer-data">appendArrayBuffer()</a></code>, <code><a href="#widl-SourceBuffer-appendStream-void-Stream-stream-unsigned-long-long-maxSize">appendStream()</a></code> and <code><a href="#widl-MediaSource-endOfStream-void-EndOfStreamError-error">endOfStream()</a></code> can update the duration under certain circumstances.</p></div>
</li>
</ol>
</dd><dt id="widl-MediaSource-readyState"><code>readyState</code> of type <span class="idlAttrType"><a href="#idl-def-ReadyState" class="idlType"><code>ReadyState</code></a></span>, readonly</dt><dd>
<p>Indicates the current state of the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> object. When the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> is created <code><a href="#widl-MediaSource-readyState">readyState</a></code> must be set to <code><a href="#idl-def-ReadyState">"closed"</a></code>.
</p></dd><dt id="widl-MediaSource-sourceBuffers"><code>sourceBuffers</code> of type <span class="idlAttrType"><a href="#idl-def-SourceBufferList" class="idlType"><code>SourceBufferList</code></a></span>, readonly</dt><dd>
Contains the list of <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects associated with this <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a>. When <code><a href="#widl-MediaSource-readyState">readyState</a></code> equals <code><a href="#idl-def-ReadyState">"closed"</a></code> this list will be empty. Once <code><a href="#widl-MediaSource-readyState">readyState</a></code> transitions to <code><a href="#idl-def-ReadyState">"open"</a></code> SourceBuffer objects can be added to this list by using <code><a href="#widl-MediaSource-addSourceBuffer-SourceBuffer-DOMString-type">addSourceBuffer()</a></code>.
</dd></dl></section><section id="methods"><h3><span class="secno">3.2 </span>Methods</h3><dl class="methods"><dt id="widl-MediaSource-addSourceBuffer-SourceBuffer-DOMString-type"><code>addSourceBuffer</code></dt><dd>
<p>Adds a new <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> to <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>.</p>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">type</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a></code></div><p>When this method is invoked, the user agent must run the following steps:</p><ol class="method-algorithm">
<li>If <var>type</var> is null or an empty string then throw an <code><a href="http://dom.spec.whatwg.org/#dom-domexception-invalid_access_err">INVALID_ACCESS_ERR</a></code> exception and abort these steps.</li>
<li>If <var>type</var> contains a MIME type that is not supported or contains a MIME type that is not supported with the types specified for the other <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>, then throw a <code><a href="http://dom.spec.whatwg.org/#dom-domexception-not_supported_err">NOT_SUPPORTED_ERR</a></code> exception and abort these steps.</li>
<li>If the user agent can't handle any more SourceBuffer objects then throw a <code><a href="http://dom.spec.whatwg.org/#dom-domexception-quota_exceeded_err">QUOTA_EXCEEDED_ERR</a></code> exception and abort these steps.</li>
<li>If the <code><a href="#widl-MediaSource-readyState">readyState</a></code> attribute is not in the <code><a href="#idl-def-ReadyState">"open"</a></code> state then throw an <code><a href="http://dom.spec.whatwg.org/#dom-domexception-invalid_state_err">INVALID_STATE_ERR</a></code> exception and abort these steps.</li>
<li>Create a new <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object and associated resources.</li>
<li>Add the new object to <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> and <a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-addsourcebuffer">addsourcebuffer</a></code> at <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>.</li>
<li>Return the new object.</li>
</ol></dd><dt id="widl-MediaSource-endOfStream-void-EndOfStreamError-error"><code>endOfStream</code></dt><dd>
<p>Signals the end of the stream.</p>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">error</td><td class="prmType"><code><a href="#idl-def-EndOfStreamError" class="idlType"><code>EndOfStreamError</code></a></code></td><td class="prmNullFalse">✘</td><td class="prmOptTrue">✔</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a>void</a></code></div><p>When this method is invoked, the user agent must run the following steps:</p><ol class="method-algorithm">
<li>If the <code><a href="#widl-MediaSource-readyState">readyState</a></code> attribute is not in the <code><a href="#idl-def-ReadyState">"open"</a></code> state then throw an <code><a href="http://dom.spec.whatwg.org/#dom-domexception-invalid_state_err">INVALID_STATE_ERR</a></code> exception and abort these steps.</li>
<li>Change the <code><a href="#widl-MediaSource-readyState">readyState</a></code> attribute value to <code><a href="#idl-def-ReadyState">"ended"</a></code>.</li>
<li>
<a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">Queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-sourceended">sourceended</a></code> at the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a>.</li>
<li><dl class="switch">
<dt>If <var>error</var> is not set, null, or an empty string</dt>
<dd>
<ol>
<li>Run the <a href="#duration-change-algorithm">duration change algorithm</a> with <var>new duration</var> set to the highest end timestamp across all <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>.<br>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">This allows the duration to properly reflect the end of the appended media segments. For example, if the duration was explicitly set to 10 seconds and only media segments for 0 to 5 seconds were appended before endOfStream() was called, then the duration will get updated to 5 seconds.</p></div>
</li>
<li>Notify the media element that it now has all of the media data. Playback should continue until all the media passed in via <code><a href="#widl-SourceBuffer-appendArrayBuffer-void-ArrayBuffer-data">appendArrayBuffer()</a></code> and <code><a href="#widl-SourceBuffer-appendStream-void-Stream-stream-unsigned-long-long-maxSize">appendStream()</a></code> has been played.</li>
</ol>
</dd>
<dt>If <var>error</var> is set to <code><a href="#idl-def-EndOfStreamError">"network"</a></code>
</dt>
<dd>
<dl class="switch">
<dt>If the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute equals <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_nothing">HAVE_NOTHING</a></code>
</dt>
<dd>Run the steps of the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#concept-media-load-resource">resource fetch algorithm</a>.</dd>
<dt>If the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute is greater than <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_nothing">HAVE_NOTHING</a></code>
</dt>
<dd>Run the "<i>If the connection is interrupted after some media data has been received, causing the user agent to give up trying to fetch the resource</i>" steps of the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#concept-media-load-resource">resource fetch algorithm</a>.</dd>
</dl>
</dd>
<dt>If <var>error</var> is set to <code><a href="#idl-def-EndOfStreamError">"decode"</a></code>
</dt>
<dd>
<dl class="switch">
<dt>If the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute equals <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_nothing">HAVE_NOTHING</a></code>
</dt>
<dd>Run the "<i>If the media data can be fetched but is found by inspection to be in an unsupported format, or can otherwise not be rendered at all</i>" steps of the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#concept-media-load-resource">resource fetch algorithm</a>.</dd>
<dt>If the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute is greater than <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_nothing">HAVE_NOTHING</a></code>
</dt>
<dd>Run the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#fatal-decode-error">media data is corrupted</a> steps of the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#concept-media-load-resource">resource fetch algorithm</a>.</dd>
</dl>
</dd>
<dt>Otherwise</dt>
<dd>Throw an <code><a href="http://dom.spec.whatwg.org/#dom-domexception-invalid_access_err">INVALID_ACCESS_ERR</a></code> exception.</dd>
</dl>
</li>
</ol></dd><dt id="widl-MediaSource-getSourceBuffer-SourceBuffer-VideoTrack-videoTrack"><code>getSourceBuffer</code></dt><dd>
<p>Gets the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object that created a specific <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#videotrack">VideoTrack</a></code>.</p>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">videoTrack</td><td class="prmType"><code><a>VideoTrack</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a></code>, nullable</div><p>When this method is invoked, the user agent must run the following steps:</p><ol class="method-algorithm">
<li>If <var>videoTrack</var> was not created by any <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> then return null.</li>
<li>Return the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> that created <var>videoTrack</var>.
</li></ol></dd><dt id="widl-MediaSource-getSourceBuffer-SourceBuffer-AudioTrack-audioTrack"><code>getSourceBuffer</code></dt><dd>
<p>Gets the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object that created a specific <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#audiotrack">AudioTrack</a></code>.</p>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">audioTrack</td><td class="prmType"><code><a>AudioTrack</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a></code>, nullable</div><p>When this method is invoked, the user agent must run the following steps:</p><ol class="method-algorithm">
<li>If <var>audioTrack</var> was not created by any <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> then return null.</li>
<li>Return the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> that created <var>audioTrack</var>.
</li></ol></dd><dt id="widl-MediaSource-getSourceBuffer-SourceBuffer-TextTrack-textTrack"><code>getSourceBuffer</code></dt><dd>
<p>Gets the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object that created a specific <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#texttrack">TextTrack</a></code>.</p>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">textTrack</td><td class="prmType"><code><a>TextTrack</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a></code>, nullable</div><p>When this method is invoked, the user agent must run the following steps:</p><ol class="method-algorithm">
<li>If <var>textTrack</var> was not created by any <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> then return null.</li>
<li>Return the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> that created <var>textTrack</var>.
</li></ol></dd><dt id="widl-MediaSource-isTypeSupported-bool-DOMString-type"><code>isTypeSupported</code>, static</dt><dd>
<p>Check to see whether the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> is capable of creating <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects for the the specified MIME type.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">
If true is returned from this method, it only indicates that the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> implementation is capable of creating <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects for the specified MIME type. An <code><a href="#widl-MediaSource-addSourceBuffer-SourceBuffer-DOMString-type">addSourceBuffer()</a></code> call may still fail if sufficient resources are not available to support the addition of a new <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a>.
</p></div>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">
This method returning true implies that HTMLMediaElement.canPlayType() will return "maybe" or "probably" since it does not make sense for a <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> to support a type the HTMLMediaElement knows it cannot play.
</p></div>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">type</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a>bool</a></code></div><p>When this method is invoked, the user agent must run the following steps:</p><ol class="method-algorithm">
<li>If <var>type</var> is an empty string, then return false.</li>
<li>If <var>type</var> does not contain a valid MIME type string, then return false.</li>
<li>If <var>type</var> contains a media type or media subtype that the MediaSource does not support, then return false.</li>
<li>If <var>type</var> contains at a codec that the MediaSource does not support, then return false.</li>
<li>If the MediaSource does not support the specified combination of media type, media subtype, and codecs then return false.</li>
<li>Return true.</li>
</ol></dd><dt id="widl-MediaSource-removeSourceBuffer-void-SourceBuffer-sourceBuffer"><code>removeSourceBuffer</code></dt><dd>
<p>Removes a <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> from <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>.</p>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">sourceBuffer</td><td class="prmType"><code><a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a>void</a></code></div><p>When this method is invoked, the user agent must run the following steps:</p><ol class="method-algorithm">
<li>If <var>sourceBuffer</var> is null then throw an <code><a href="http://dom.spec.whatwg.org/#dom-domexception-invalid_access_err">INVALID_ACCESS_ERR</a></code> exception and abort these steps.</li>
<li>If <var>sourceBuffer</var> specifies an object that is not in <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> then throw a <code><a href="http://dom.spec.whatwg.org/#dom-domexception-not_found_err">NOT_FOUND_ERR</a></code> exception and abort these steps.</li>
<li>Remove track information from <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-audiotracks">audioTracks</a></code>, <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-videotracks">videoTracks</a></code>, and <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-texttracks">textTracks</a></code> for all tracks associated with <var>sourceBuffer</var> and <a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <a href="http://www.w3.org/TR/html5/embedded-content-0.html#handler-tracklist-onchange">change</a> at the modified lists.</li>
<li>If <var>sourceBuffer</var> is in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>, then remove it from <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> and <a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-removesourcebuffer">removesourcebuffer</a></code> at <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>.</li>
<li>Remove <var>sourceBuffer</var> from <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code> and <a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-removesourcebuffer">removesourcebuffer</a></code> at <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>.</li>
<li>Destroy all resources for <var>sourceBuffer</var>.</li>
</ol></dd><dt id="widl-MediaSource-setTrackInfo-void-VideoTrack-track-DOMString-kind-DOMString-language"><code>setTrackInfo</code></dt><dd>
<p>Set the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-videotrack-kind">kind</a></code> and <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-videotrack-language">language</a></code> of the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#videotrack">VideoTrack</a></code> <var>track</var>.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">This method would be unnecessary if the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-videotrack-kind">kind</a></code> and <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-videotrack-language">language</a></code> attributes of <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#videotrack">VideoTrack</a></code> were not read-only.</p></div>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">track</td><td class="prmType"><code><a>VideoTrack</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">kind</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">language</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a>void</a></code></div></dd><dt id="widl-MediaSource-setTrackInfo-void-AudioTrack-track-DOMString-kind-DOMString-language"><code>setTrackInfo</code></dt><dd>
<p>Set the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-audiotrack-kind">kind</a></code> and <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-audiotrack-language">language</a></code> of the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#audiotrack">AudioTrack</a></code> <var>track</var>.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">This method would be unnecessary if the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-audiotrack-kind">kind</a></code> and <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-audiotrack-language">language</a></code> attributes of <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#audiotrack">AudioTrack</a></code> were not read-only.</p></div>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">track</td><td class="prmType"><code><a>AudioTrack</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">kind</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">language</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a>void</a></code></div></dd><dt id="widl-MediaSource-setTrackInfo-void-TextTrack-track-DOMString-kind-DOMString-language"><code>setTrackInfo</code></dt><dd>
<p>Set the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-texttrack-kind">kind</a></code> and <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-texttrack-language">language</a></code> of the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#texttrack">TextTrack</a></code> <var>track</var>.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">This method would be unnecessary if the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-texttrack-kind">kind</a></code> and <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-texttrack-language">language</a></code> attributes of <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#texttrack">TextTrack</a></code> were not read-only.</p></div>
<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">track</td><td class="prmType"><code><a>TextTrack</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">kind</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">language</td><td class="prmType"><code><a>DOMString</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></section>
<section id="mediasource-events">
<h3><span class="secno">3.3 </span>Event Summary</h3>
<table class="old-table">
<thead>
<tr>
<th>Event name</th>
<th>Interface</th>
<th>Dispatched when...</th>
</tr>
</thead>
<tbody>
<tr>
<td><dfn id="dom-evt-sourceopen"><code>sourceopen</code></dfn></td>
<td><code>Event</code></td>
<td><code><a href="#widl-MediaSource-readyState">readyState</a></code> transitions from <code><a href="#idl-def-ReadyState">"closed"</a></code> to <code><a href="#idl-def-ReadyState">"open"</a></code> or from <code><a href="#idl-def-ReadyState">"ended"</a></code> to <code><a href="#idl-def-ReadyState">"open"</a></code>.</td>
</tr>
<tr>
<td><dfn id="dom-evt-sourceended"><code>sourceended</code></dfn></td>
<td><code>Event</code></td>
<td><code><a href="#widl-MediaSource-readyState">readyState</a></code> transitions from <code><a href="#idl-def-ReadyState">"open"</a></code> to <code><a href="#idl-def-ReadyState">"ended"</a></code>.</td>
</tr>
<tr>
<td><dfn id="dom-evt-sourceclose"><code>sourceclose</code></dfn></td>
<td><code>Event</code></td>
<td><code><a href="#widl-MediaSource-readyState">readyState</a></code> transitions from <code><a href="#idl-def-ReadyState">"open"</a></code> to <code><a href="#idl-def-ReadyState">"closed"</a></code> or <code><a href="#idl-def-ReadyState">"ended"</a></code> to <code><a href="#idl-def-ReadyState">"closed"</a></code>.</td>
</tr>
</tbody>
</table>
</section>
<section id="mediasource-algorithms">
<h3><span class="secno">3.4 </span>Algorithms</h3>
<section id="mediasource-attach">
<h4><span class="secno">3.4.1 </span>Attaching to a media element</h4>
<p> A <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a> object can be attached to a media element by assigning a <a href="#mediasource-object-url">MediaSource object URL</a> to the media element <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#attr-media-src">src</a></code> attribute or the src attribute of a <source> inside a media element. A <a href="#mediasource-object-url">MediaSource object URL</a> is created by passing a MediaSource object to <code><a href="#widl-URL-createObjectURL-DOMString-MediaSource-mediaSource">createObjectURL()</a></code>.</p>
<p>If the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#concept-media-load-resource">resource fetch algorithm</a> absolute URL matches the MediaSource object URL, run the following steps right before the "Perform a potentially
CORS-enabled fetch" step in the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#concept-media-load-resource">resource fetch algorithm</a>.</p>
<dl class="switch">
<dt>If <code><a href="#widl-MediaSource-readyState">readyState</a></code> is NOT set to <code><a href="#idl-def-ReadyState">"closed"</a></code></dt>
<dd>Run the steps of the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#concept-media-load-resource">resource fetch algorithm</a>.</dd>
<dt>Otherwise</dt>
<dd>
<ol>
<li>Set the <code><a href="#widl-MediaSource-readyState">readyState</a></code> attribute to <code><a href="#idl-def-ReadyState">"open"</a></code>.</li>
<li>
<a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">Queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-sourceopen">sourceopen</a></code> at the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a>.</li>
<li>Allow the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#concept-media-load-resource">resource fetch algorithm</a> to progress based on data passed in via <code><a href="#widl-SourceBuffer-appendArrayBuffer-void-ArrayBuffer-data">appendArrayBuffer()</a></code> and <code><a href="#widl-SourceBuffer-appendStream-void-Stream-stream-unsigned-long-long-maxSize">appendStream()</a></code>.</li>
</ol>
</dd>
</dl>
</section>
<section id="mediasource-detach">
<h4><span class="secno">3.4.2 </span>Detaching from a media element</h4>
<p>The following steps are run in any case where the media element is going to transition to <a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-network_empty">NETWORK_EMPTY</a> and <a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <a href="http://www.w3.org/TR/html5/embedded-content-0.html#event-mediacontroller-emptied">emptied</a> at the media element. These steps should be run right before the transition.</p>
<ol>
<li>Set the <code><a href="#widl-MediaSource-readyState">readyState</a></code> attribute to <code><a href="#idl-def-ReadyState">"closed"</a></code>.</li>
<li>Set the <code><a href="#widl-MediaSource-duration">duration</a></code> attribute to NaN.</li>
<li>Remove all the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects from <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>.</li>
<li>
<a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">Queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-removesourcebuffer">removesourcebuffer</a></code> at <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>.</li>
<li>Remove all the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects from <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>.</li>
<li>
<a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">Queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-removesourcebuffer">removesourcebuffer</a></code> at <code><a href="#widl-MediaSource-sourceBuffers">sourceBuffers</a></code>.</li>
<li>
<a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">Queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-sourceclose">sourceclose</a></code> at the <a href="#idl-def-MediaSource" class="idlType"><code>MediaSource</code></a>.</li>
</ol>
</section>
<section id="mediasource-seeking">
<h4><span class="secno">3.4.3 </span>Seeking</h4>
<p>Run the following steps as part of the "<i>Wait until the user agent has established whether or not the media data for the new playback position is available, and, if it is, until it has decoded enough data to play back that position"</i> step of the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-seek">seek algorithm</a>:</p>
<ol>
<li>The media element looks for <a href="#media-segment">media segments</a> containing the <var>new playback position</var> in each <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> object in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>.
<dl class="switch">
<dt>If one or more of the objects in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> is missing <a href="#media-segment">media segments</a> for the <var>new playback position</var>
</dt>
<dd>
<ol>
<li>Set the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_metadata">HAVE_METADATA</a></code>.</li>
<li>The media element waits for the necessary <a href="#media-segment">media segments</a> to be passed to <code><a href="#widl-SourceBuffer-appendArrayBuffer-void-ArrayBuffer-data">appendArrayBuffer()</a></code> or <code><a href="#widl-SourceBuffer-appendStream-void-Stream-stream-unsigned-long-long-maxSize">appendStream()</a></code>.
<div class="note"><div class="note-title"><span>Note</span></div><p class="">The web application can use <code><a href="#widl-SourceBuffer-buffered">buffered</a></code> to determine what the media element needs to resume playback.</p></div>
</li>
</ol>
</dd>
<dt>Otherwise</dt>
<dd>Continue</dd>
</dl>
</li>
<li>The media element resets all decoders and initializes each one with data from the appropriate <a href="#init-segment">initialization segment</a>.</li>
<li>The media element feeds data from the <a href="#media-segment">media segments</a> into the decoders until the <var>new playback position</var> is reached.</li>
<li>Resume the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-seek">seek algorithm</a> at the "<i>Await a stable state</i>" step.</li>
</ol>
</section>
<section id="buffer-monitoring">
<h4><span class="secno">3.4.4 </span>SourceBuffer Monitoring</h4>
<p>The following steps are periodically run during playback to make sure that all of the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> objects in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> have enough data to ensure uninterrupted playback. Appending new segments and changes to <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> also cause these steps to run because they affect the conditions that trigger state transitions.</p>
<div class="note"><div class="note-title"><span>Note</span></div><p class="">The web application can monitor changes in <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> to drive <a href="#media-segment">media segment</a> appending.</p></div>
<div class="issue"><div class="issue-title"><span>Issue 3</span></div><p class=""><a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=18592">Bug 18592</a> - How much is "enough data to ensure uninterrupted playback"</p></div>
<dl class="switch">
<dt>If <code><a href="#widl-SourceBuffer-buffered">buffered</a></code> for all objects in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> do not contain <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#timeranges">TimeRanges</a></code> for the current playback position:</dt>
<dd>
<ol>
<li>Set the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_metadata">HAVE_METADATA</a></code>.</li>
<li>If this is the first transition to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_metadata">HAVE_METADATA</a></code>, then <a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#event-media-loadedmetadata">loadedmetadata</a></code> at the media element.</li>
<li>Abort these steps.</li>
</ol>
</dd>
<dt>If <code><a href="#widl-SourceBuffer-buffered">buffered</a></code> for all objects in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> contain <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#timeranges">TimeRanges</a></code> that include the current playback position and enough data to ensure uninterrupted playback:</dt>
<dd>
<ol>
<li>Set the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_enough_data">HAVE_ENOUGH_DATA</a></code>.</li>
<li>
<a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">Queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#event-media-canplaythrough">canplaythrough</a></code> at the media element.</li>
<li>Playback may resume at this point if it was previously suspended by a transition to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_current_data">HAVE_CURRENT_DATA</a></code>.</li>
<li>Abort these steps.</li>
</ol>
</dd>
<dt>If <code><a href="#widl-SourceBuffer-buffered">buffered</a></code> for at least one object in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> contains a <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#timeranges">TimeRange</a></code> that includes the current playback position but not enough data to ensure uninterrupted playback:</dt>
<dd>
<ol>
<li>Set the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_future_data">HAVE_FUTURE_DATA</a></code>.</li>
<li>If the previous value of <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> was less than <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_future_data">HAVE_FUTURE_DATA</a></code>, then <a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#event-media-canplay">canplay</a></code> at the media element.</li>
<li>Playback may resume at this point if it was previously suspended by a transition to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_current_data">HAVE_CURRENT_DATA</a></code>.</li>
<li>Abort these steps.</li>
</ol>
</dd>
<dt>If <code><a href="#widl-SourceBuffer-buffered">buffered</a></code> for at least one object in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> contains a <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#timeranges">TimeRange</a></code> that ends at the current playback position and does not have a range covering the time immediately after the current position:</dt>
<dd>
<ol>
<li>Set the <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-readystate">HTMLMediaElement.readyState</a></code> attribute to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_current_data">HAVE_CURRENT_DATA</a></code>.</li>
<li>If this is the first transition to <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-media-have_current_data">HAVE_CURRENT_DATA</a></code>, then <a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="http://www.w3.org/TR/html5/embedded-content-0.html#event-media-loadeddata">loadeddata</a></code> at the media element.</li>
<li>Playback is suspended at this point since the media element doesn't have enough data to advance the timeline.</li>
<li>Abort these steps.</li>
</ol>
</dd>
</dl>
</section>
<section id="active-source-buffer-changes">
<h4><span class="secno">3.4.5 </span>Changes to selected/enabled track state</h4>
<p>During playback <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code> needs to be updated if the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-videotrack-selected">selected video track</a>, the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-audiotrack-enabled">enabled audio tracks</a>, or a text track <a href="http://www.w3.org/TR/html5/embedded-content-0.html#dom-texttrack-mode">mode</a> changes. When one or more of these changes occur the following steps need to be followed.</p>
<dl class="switch">
<dt>If the selected video track changes, then run the following steps:</dt>
<dd>
<ol>
<li>If the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> associated with the previously selected video track is not associated with any other enabled tracks, run the following steps:
<ol>
<li>Remove the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> from <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>.</li>
<li>
<a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">Queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-removesourcebuffer">removesourcebuffer</a></code> at <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>
</li>
</ol>
</li>
<li>If the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> associated with the newly selected video track is not already in <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>, run the following steps:
<ol>
<li>Add the <a href="#idl-def-SourceBuffer" class="idlType"><code>SourceBuffer</code></a> to <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>.</li>
<li>
<a href="http://www.w3.org/TR/html5/webappapis.html#queue-a-task">Queue a task</a> to <a href="http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">fire a simple event</a> named <code><a href="#dom-evt-addsourcebuffer">addsourcebuffer</a></code> at <code><a href="#widl-MediaSource-activeSourceBuffers">activeSourceBuffers</a></code>
</li>
</ol>
</li>
</ol>