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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE html PUBLIC '-//W3C//DTD XHTML 1.0 Transitional//EN' 'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'>
<html xmlns="http://www.w3.org/1999/xhtml" dir="ltr">
<head>
  <meta name="generator" content="HTML Tidy for Linux/x86 (vers 11 February 2007), see www.w3.org" />
  <title>WebRTC 1.0: Real-time Communication Between Browsers</title>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />  
<style type="text/css">
/*****************************************************************
 * Styles specific to WebRTC spec
 *****************************************************************/
pre { white-space: pre-wrap; }
table { border-collapse: collapse; border-style: hidden hidden none hidden; }
table thead, table tbody { border-bottom: solid #90B8DE; }
table tbody th { text-align: left; }
table tbody th:first-child { border-left: solid #90B8DE; }
table td, table th { border-left: solid #90B8DE; border-right: solid #90B8DE; border-bottom: solid thin #90B8DE; vertical-align: top; padding: 0.2em; }
.note { color: green; }
.example { display: block; color: #222222; background: #FCFCFC; border-left: double; margin-left: 2em; padding-left: 1em; }


/*****************************************************************
 * ReSpec CSS
 * Robin Berjon (robin at berjon dot com)
 * v0.05 - 2009-07-31
 *****************************************************************/


/* --- 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;
}

code {
    color:  #ff4500;
}


/* --- 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 {
    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 {
    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%;
}

/* --- TOC --- */
.toc a {
    text-decoration:    none;
}

a .secno {
    color:  #000;
}

/* --- 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;
}

/* --- EXAMPLES --- */
pre.example {
    border-top: 1px solid #ff4500;
    border-bottom: 1px solid #ff4500;
    padding:    1em;
    margin-top: 1em;
}

pre.example::before {
    content:    "Example";
    display:    block;
    width:      150px;
    background: #ff4500;
    color:  #fff;
    font-family:    initial;
    padding:    3px;
    font-weight:    bold;
    margin: -1em 0 1em -1em;
}

/* --- EDITORIAL NOTES --- */
.issue {
    padding:    1em;
    margin: 1em 0em 0em;
    border: 1px solid #f00;
    background: #ffc;
}

.issue::before {
    content:    "Issue";
    display:    block;
    width:  150px;
    margin: -1.5em 0 0.5em 0;
    font-weight:    bold;
    border: 1px solid #f00;
    background: #fff;
    padding:    3px 1em;
}

.note {
    margin: 1em 0em 0em;
    padding:    1em;
    border: 2px solid #cff6d9;
    background: #e2fff0;
}

.note::before {
    content:    "Note";
    display:    block;
    width:  150px;
    margin: -1.5em 0 0.5em 0;
    font-weight:    bold;
    border: 1px solid #cff6d9;
    background: #fff;
    padding:    3px 1em;
}

/* --- Best Practices --- */
div.practice {
    border: solid #bebebe 1px;
    margin: 2em 1em 1em 2em;
}

span.practicelab {
    margin: 1.5em 0.5em 1em 1em;
    font-weight: bold;
    font-style: italic;
}

span.practicelab   { background: #dfffff; }

span.practicelab {
    position: relative;
    padding: 0 0.5em;
    top: -1.5em;
}

p.practicedesc {
    margin: 1.5em 0.5em 1em 1em;
}

@media screen {
    p.practicedesc {
        position: relative;
        top: -2em;
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</style><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet" type="text/css" charset="utf-8" /></head>

<body style="display: inherit; "><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">WebRTC 1.0: Real-time Communication Between Browsers</h1><h2 id="w3c-working-draft-27-october-2011">W3C Working Draft 27 October 2011</h2><dl><dt>This version:</dt><dd><a href="http://www.w3.org/TR/2011/WD-webrtc-20111027/">http://www.w3.org/TR/2011/WD-webrtc-20111027/</a></dd><dt>Latest published version:</dt><dd><a href="http://www.w3.org/TR/webrtc/">http://www.w3.org/TR/webrtc/</a></dd><dt>Latest editor's draft:</dt><dd><a href="http://dev.w3.org/2011/webrtc/editor/webrtc.html">http://dev.w3.org/2011/webrtc/editor/webrtc.html</a></dd><dt>Previous version:</dt><dd>none</dd><dt>Editors:</dt><dd><span>Adam Bergkvist</span>, Ericsson</dd>
<dd><span>Daniel C. Burnett</span>, Voxeo</dd>
<dd><span>Cullen Jennings</span>, Cisco</dd>
<dd><span>Anant Narayanan</span>, Mozilla</dd>
</dl><p class="copyright">Initial Author of this Specification was Ian Hickson, Google Inc., with the following copyright statement:<br /> © Copyright 2004-2011 Apple Computer, Inc., Mozilla Foundation, and Opera Software ASA. You are granted a license to use, reproduce and create derivative works of this document.</p> <p class="copyright">All subsequent changes since 26 July 2011 done by the W3C WebRTC Working Group are under the following <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>:<br />© 2011 <a href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. <a href="http://www.w3.org/Consortium/Legal/copyright-documents">Document use</a>  rules apply.</p> <p class="copyright">For the entire publication on the W3C site the <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a> and <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> rules apply.</p><hr /></div>
  <div id="abstract" class="introductory section"><h2>Abstract</h2>
    <p>This document defines a set of APIs that allow local media, including audio and video, to be requested from a platform, media to be sent over the network to another browser or device implementing the appropriate set of real-time protocols, and media received from another browser or device to be processed and displayed locally. This specification is being developed in conjunction with a protocol specification developed by the IETF RTCWEB group.</p>
  </div><div id="sotd" class="introductory section"><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 W3C publications and the latest revision of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a> at http://www.w3.org/TR/.</em></p>
   <p>This document is a First Public Working Draft and is not complete.
   It is subject to major changes and, while early experimentations are
   encouraged, it is therefore not intended for implementation. The API
   is based on preliminary work done in the WHATWG. The Web Real-Time
   Communications Working Group expects this specification to evolve
   significantly based on:</p>
  <ul>
    <li>The outcomes of ongoing exchanges in the companion RTCWEB group
    at IETF to define the set of protocols that, together with this
    document, will enable real-time communications in Web browsers.</li>
    <li>Privacy issues that arise when exposing local capabilities and
    local streams.</li>
    <li>Technical discussions within the group, on the data channel in
    particular.</li>
    <li>Experience gained through early experimentations.</li>
    <li>Feedback received from other groups and individuals.</li>
  </ul>
  <p>As the specification matures, the group hopes to strike the right
  balance between a low-level API that would enable interested parties
  to tweak potentially complex system parameters, and a more high-level
  API that Web developers can use without <em>a priori</em> technical
  knowledge about real-time communications.</p>
<p>This document was published by the <a href="http://www.w3.org/2011/04/webrtc/">Web Real-Time Communications Working Group</a> as a Working Draft. This document is intended to become a W3C Recommendation. If you wish to make comments regarding this document, please send them to <a href="mailto:public-webrtc@w3.org">public-webrtc@w3.org</a> (<a href="mailto:public-webrtc-request@w3.org?subject=subscribe">subscribe</a>, <a href="http://lists.w3.org/Archives/Public/public-webrtc/">archives</a>). All feedback is welcome.</p><p>Publication as a Working Draft does not imply endorsement by the W3C 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 W3C Patent Policy</a>. W3C maintains a <a href="http://www.w3.org/2004/01/pp-impl/47318/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 disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>.</p></div><div id="toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#intro" class="tocxref"><span class="secno">1. </span>Introduction</a></li><li class="tocline"><a href="#local-content" class="tocxref"><span class="secno">2. </span>Obtaining local multimedia content</a><ul class="toc"><li class="tocline"><a href="#local-content-definition" class="tocxref"><span class="secno">2.1 </span>Definition</a><ul class="toc"><li class="tocline"><a href="#navigatorusermedia" class="tocxref"><span class="secno">2.1.1 </span>NavigatorUserMedia</a><ul class="toc"><li class="tocline"><a href="#methods" class="tocxref"><span class="secno">2.1.1.1 </span>Methods</a></li></ul></li><li class="tocline"><a href="#mediastreamoptions" class="tocxref"><span class="secno">2.1.2 </span>MediaStreamOptions</a><ul class="toc"><li class="tocline"><a href="#attributes" class="tocxref"><span class="secno">2.1.2.1 </span>Attributes</a></li></ul></li><li class="tocline"><a href="#navigatorusermediasuccesscallback" class="tocxref"><span class="secno">2.1.3 </span>NavigatorUserMediaSuccessCallback</a><ul class="toc"><li class="tocline"><a href="#methods-1" class="tocxref"><span class="secno">2.1.3.1 </span>Methods</a></li></ul></li><li class="tocline"><a href="#navigatorusermediaerror-and-navigatorusermediaerrorcallback" class="tocxref"><span class="secno">2.1.4 </span>NavigatorUserMediaError and NavigatorUserMediaErrorCallback</a><ul class="toc"><li class="tocline"><a href="#attributes-1" class="tocxref"><span class="secno">2.1.4.1 </span>Attributes</a></li><li class="tocline"><a href="#constants" class="tocxref"><span class="secno">2.1.4.2 </span>Constants</a></li><li class="tocline"><a href="#methods-2" class="tocxref"><span class="secno">2.1.4.3 </span>Methods</a></li></ul></li></ul></li><li class="tocline"><a href="#examples" class="tocxref"><span class="secno">2.2 </span>Examples</a></li></ul></li><li class="tocline"><a href="#stream-api" class="tocxref"><span class="secno">3. </span>Stream API</a><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">3.1 </span>Introduction</a></li><li class="tocline"><a href="#interface-definitions" class="tocxref"><span class="secno">3.2 </span>Interface definitions</a><ul class="toc"><li class="tocline"><a href="#mediastream" class="tocxref"><span class="secno">3.2.1 </span>MediaStream</a><ul class="toc"><li class="tocline"><a href="#attributes-2" class="tocxref"><span class="secno">3.2.1.1 </span>Attributes</a></li><li class="tocline"><a href="#methods-3" class="tocxref"><span class="secno">3.2.1.2 </span>Methods</a></li><li class="tocline"><a href="#constants-1" class="tocxref"><span class="secno">3.2.1.3 </span>Constants</a></li></ul></li><li class="tocline"><a href="#localmediastream" class="tocxref"><span class="secno">3.2.2 </span>LocalMediaStream</a><ul class="toc"><li class="tocline"><a href="#methods-4" class="tocxref"><span class="secno">3.2.2.1 </span>Methods</a></li></ul></li><li class="tocline"><a href="#mediastreamtrack" class="tocxref"><span class="secno">3.2.3 </span>MediaStreamTrack</a><ul class="toc"><li class="tocline"><a href="#attributes-3" class="tocxref"><span class="secno">3.2.3.1 </span>Attributes</a></li></ul></li><li class="tocline"><a href="#mediastreamrecorder" class="tocxref"><span class="secno">3.2.4 </span>MediaStreamRecorder</a><ul class="toc"><li class="tocline"><a href="#methods-5" class="tocxref"><span class="secno">3.2.4.1 </span>Methods</a></li></ul></li><li class="tocline"><a href="#blobcallback" class="tocxref"><span class="secno">3.2.5 </span>BlobCallback</a><ul class="toc"><li class="tocline"><a href="#methods-6" class="tocxref"><span class="secno">3.2.5.1 </span>Methods</a></li></ul></li><li class="tocline"><a href="#url" class="tocxref"><span class="secno">3.2.6 </span>URL</a><ul class="toc"><li class="tocline"><a href="#methods-7" class="tocxref"><span class="secno">3.2.6.1 </span>Methods</a></li></ul></li></ul></li><li class="tocline"><a href="#examples-1" class="tocxref"><span class="secno">3.3 </span>Examples</a></li></ul></li><li class="tocline"><a href="#peer-to-peer-connections" class="tocxref"><span class="secno">4. </span>Peer-to-peer connections</a><ul class="toc"><li class="tocline"><a href="#peerconnection" class="tocxref"><span class="secno">4.1 </span>PeerConnection</a><ul class="toc"><li class="tocline"><a href="#attributes-4" class="tocxref"><span class="secno">4.1.1 </span>Attributes</a></li><li class="tocline"><a href="#methods-8" class="tocxref"><span class="secno">4.1.2 </span>Methods</a></li><li class="tocline"><a href="#constants-2" class="tocxref"><span class="secno">4.1.3 </span>Constants</a></li></ul></li><li class="tocline"><a href="#signalingcallback" class="tocxref"><span class="secno">4.2 </span>SignalingCallback</a><ul class="toc"><li class="tocline"><a href="#methods-9" class="tocxref"><span class="secno">4.2.1 </span>Methods</a></li></ul></li><li class="tocline"><a href="#examples-2" class="tocxref"><span class="secno">4.3 </span>Examples</a></li></ul></li><li class="tocline"><a href="#the-data-stream" class="tocxref"><span class="secno">5. </span>The data stream</a></li><li class="tocline"><a href="#garbage-collection" class="tocxref"><span class="secno">6. </span>Garbage collection</a></li><li class="tocline"><a href="#event-definitions" class="tocxref"><span class="secno">7. </span>Event definitions</a><ul class="toc"><li class="tocline"><a href="#mediastreamevent" class="tocxref"><span class="secno">7.1 </span>MediaStreamEvent</a><ul class="toc"><li class="tocline"><a href="#attributes-5" class="tocxref"><span class="secno">7.1.1 </span>Attributes</a></li><li class="tocline"><a href="#methods-10" class="tocxref"><span class="secno">7.1.2 </span>Methods</a></li></ul></li></ul></li><li class="tocline"><a href="#event-summary" class="tocxref"><span class="secno">8. </span>Event summary</a></li><li class="tocline"><a href="#application-html-peer-connection-data" class="tocxref"><span class="secno">9. </span>application/html-peer-connection-data</a></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">A. </span>Acknowledgements</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">B. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">B.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">B.2 </span>Informative references</a></li></ul></li></ul></div>

   

  <div id="intro" class="informative section">
  
<!-- OddPage -->
<h2><span class="secno">1. </span>Introduction</h2><p><em>This section is non-normative.</em></p>

  <p>There are a number of facets to video-conferencing in HTML:</p>

  <ul>
    <li>Getting a multimedia stream (video, audio, or both) from local devices (video
    cameras, microphones, Web cams) or from prerecorded files provided by the user.</li>

    <li>Recording such streams locally.</li>

    <li>Connecting to remote peers using NAT-traversal technologies such as ICE, STUN,
    and TURN.</li>

    <li>Sending the locally-produced streams to remote peers and receiving streams from
    remote peers.</li>

    <li>Displaying such streams (both the locally-produced ones and the remotely-obtained
    ones) locally using the <code>video</code> or <code>audio</code> elements.</li>

    <li>Sending arbitrary data to remote peers.</li>
  </ul>

  <p>This document defines the APIs used for these features. This specification is being developed in conjunction with a protocol specification developed by the <a href="http://datatracker.ietf.org/wg/rtcweb/">IETF RTCWEB group</a>.</p>
  </div>

  <div id="local-content" class="section">
  
<!-- OddPage -->
<h2><span class="secno">2. </span>Obtaining local multimedia content</h2>

  <div id="local-content-definition" class="section">
  <h3><span class="secno">2.1 </span>Definition</h3>

  <div id="navigatorusermedia" class="section">
  <h4><span class="secno">2.1.1 </span>NavigatorUserMedia</h4>

  <pre class="idl"><span class="idlInterface" id="idl-def-NavigatorUserMedia">[<span class="extAttr">NoInterfaceObject</span>]
interface <span class="idlInterfaceID">NavigatorUserMedia</span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-NavigatorUserMedia-getUserMedia-void-MediaStreamOptions-options-NavigatorUserMediaSuccessCallback-successCallback-NavigatorUserMediaErrorCallback-errorCallback">getUserMedia</a></span> (<span class="idlParam"><span class="idlParamType"><a href="#idl-def-MediaStreamOptions" class="idlType"><code>MediaStreamOptions</code></a>?</span> <span class="idlParamName">options</span></span>, <span class="idlParam"><span class="idlParamType"><a href="#idl-def-NavigatorUserMediaSuccessCallback" class="idlType"><code>NavigatorUserMediaSuccessCallback</code></a>?</span> <span class="idlParamName">successCallback</span></span>, <span class="idlParam">optional <span class="idlParamType"><a href="#idl-def-NavigatorUserMediaErrorCallback" class="idlType"><code>NavigatorUserMediaErrorCallback</code></a>?</span> <span class="idlParamName">errorCallback</span></span>);</span>
};</span>
</pre><div id="methods" class="section"><h5><span class="secno">2.1.1.1 </span>Methods</h5><dl class="methods"><dt id="widl-NavigatorUserMedia-getUserMedia-void-MediaStreamOptions-options-NavigatorUserMediaSuccessCallback-successCallback-NavigatorUserMediaErrorCallback-errorCallback"><code>getUserMedia</code></dt><dd>
      <p>Prompts the user for permission to use their Web cam or other video or audio
      input.</p>

      <p>The <var title="">options</var> argument is an object of type
      <code title="">MediaStreamOptions</code>. The object can contain
      the following boolean properties:
      </p>

      <dl>
        <dt>&quot;<code title="">audio</code>&quot;</dt>
        <dd>The provided media needs to include audio data.</dd>

        <dt>&quot;<code title="">video</code>&quot;</dt>
        <dd>The provided media needs to include video data.</dd>
      </dl>

      <p>If the user accepts, the <var title="">successCallback</var> is invoked, with a
      suitable <code><a href="#localmediastream">LocalMediaStream</a></code> object as
      its argument.</p>

      <p>If the user declines, the <var title="">errorCallback</var> (if any) is
      invoked.</p>

      <p>When the <a href="#widl-NavigatorUserMedia-getUserMedia-void-MediaStreamOptions-options-NavigatorUserMediaSuccessCallback-successCallback-NavigatorUserMediaErrorCallback-errorCallback">
      <code>getUserMedia()</code></a> method is called, the user agent must run the
      following steps:</p>

      <ol>
        <li>
          <p>Let <var title="">options</var> be the method's first argument.</p>
        </li>

        <li>
          <p>Let <var title="">successCallback</var> be the callback indicated by the
          method's second argument.</p>
        </li>

        <li>
          <p>Let <var title="">errorCallback</var> be the callback indicated by the
          method's third argument, if any, or null otherwise.</p>
        </li>

        <li>
          <p>If <var title="">successCallback</var> is null, abort these steps.</p>
        </li>
<!--  we could throw an exception instead (that's
   why the method doesn't return until later: so that we can add an
   exception here, or for /options/ below, without changing the
   algorithm)  -->


        <li>
          <p>Let <var title="">audio</var> be true.</p>
        </li>

        <li>
          <p>Let <var title="">video</var> be true.</p>
        </li>

        <li>
          <p>If the <var title="">audio</var> property in <var title="">options</var>
          is present and set to false, let <var title="">audio</var> be false.</p>
        </li>

        <li>
          <p>If the <var title="">video</var> property in <var title="">options</var>
          is present and set to false, let <var title="">video</var> be false.</p>
        </li>

        <li>
          <p>If both <var title="">audio</var> and <var title="">video</var> are still
          false, then throw a <code>NOT_SUPPORTED_ERR</code> exception and abort these
          steps.</p>
        </li>

        <li>
          <p>Return, and run the remaining steps asynchronously.</p>
        </li>

        <li>
          <p>Optionally, e.g. based on a previously-established user preference, for
          security reasons, or due to platform limitations, jump to the step labeled
          <em>failure</em> below.</p>
        </li>

        <li>
          <p>Prompt the user in a user-agent-specific manner for permission to provide
          the entry script's origin with a <code><a href="#localmediastream">LocalMediaStream</a></code> object representing a media
          stream.</p>

          <p>If <var title="">audio</var> is true, then the provided media should include
          an audio track. If <var title="">audio</var> is false, then the provided media
          must not include an audio track.</p>

          <p>If <var title="">video</var> is true, then the provided media should include
          a video track. If <var title="">video</var> is false, then the provided media
          must not include a video track.</p>

          <p>User agents are encouraged to default to using the user's primary or system
          default camera and/or microphone (as appropriate) to generate the media stream.
          User agents may allow users to use any media source, including pre-recorded
          media files.</p>

          <p>User agents may wish to offer the user more control over the provided media.
          For example, a user agent could offer to enable a camera light or flash, or to
          change settings such as the frame rate or shutter speed.</p>

          <p>If the user grants permission to use local recording devices, user agents
          are encouraged to include a prominent indicator that the devices are &quot;hot&quot;
          (i.e. an &quot;on-air&quot; or &quot;recording&quot; indicator).</p>

          <p>If the user denies permission, jump to the step labeled <em>failure</em>
          below. If the user never responds, this algorithm stalls on this step.</p>
        </li>

        <li>
          <p>Let <var title="">stream</var> be the <code><a href="#localmediastream">LocalMediaStream</a></code> object for which the user
          granted permission.</p>
        </li>

        <li>
          <p>Queue a task to invoke <var title="">successCallback</var> with
          <var title="">stream</var> as its argument.</p>
        </li>

        <li>
          <p>Abort these steps.</p>
        </li>

        <li>
          <p><em>Failure</em>: If <var title="">errorCallback</var> is null, abort these
          steps.</p>
        </li>

        <li>
          <p>Let <var title="">error</var> be a new <code><a href="#navigatorusermediaerror-and-navigatorusermediaerrorcallback">NavigatorUserMediaError</a></code> object whose
          <code title="dom-NavigatorUserMediaError-code"><a href="#widl-NavigatorUserMediaError-code">code</a></code> attribute has the numeric
          value 1 (<code title="dom-NavigatorUserMediaError-PERMISSION_DENIED"><a href="#widl-NavigatorUserMediaError-PERMISSION_DENIED">PERMISSION_DENIED</a></code>).</p>
        </li>

        <li>
          <p>Queue a task to invoke <var title="">errorCallback</var> with
          <var title="">error</var> as its argument.</p>
        </li>
      </ol>

      <p>The task source for these <span title="concept-task">tasks</span>
      is the user interaction task source.</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">options</td><td class="prmType"><code><a href="#idl-def-MediaStreamOptions" class="idlType"><code>MediaStreamOptions</code></a></code></td><td class="prmNullTrue">✔</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">successCallback</td><td class="prmType"><code><a href="#idl-def-NavigatorUserMediaSuccessCallback" class="idlType"><code>NavigatorUserMediaSuccessCallback</code></a></code></td><td class="prmNullTrue">✔</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">errorCallback</td><td class="prmType"><code><a href="#idl-def-NavigatorUserMediaErrorCallback" class="idlType"><code>NavigatorUserMediaErrorCallback</code></a></code></td><td class="prmNullTrue">✔</td><td class="prmOptTrue">✔</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>

  <pre class="idl"><span class="idlImplements"><a>Navigator</a> implements <a href="#idl-def-NavigatorUserMedia" class="idlType"><code>NavigatorUserMedia</code></a>;</span></pre><div class="idlImplementsDesc"><p>All instances of the <code><a>Navigator</a></code> type are defined to also implement the <a href="#idl-def-NavigatorUserMedia" class="idlType"><code>NavigatorUserMedia</code></a> interface.</p></div>
  </div>

  <div id="mediastreamoptions" class="section">
  <h4><span class="secno">2.1.2 </span>MediaStreamOptions</h4>

  <pre class="idl"><span class="idlInterface" id="idl-def-MediaStreamOptions">[<span class="extAttr">NoInterfaceObject</span>]
interface <span class="idlInterfaceID">MediaStreamOptions</span> {
<span class="idlAttribute">    attribute <span class="idlAttrType"><a>boolean</a></span> <span class="idlAttrName"><a href="#widl-MediaStreamOptions-audio">audio</a></span>;</span>
<span class="idlAttribute">    attribute <span class="idlAttrType"><a>boolean</a></span> <span class="idlAttrName"><a href="#widl-MediaStreamOptions-video">video</a></span>;</span>
};</span>
</pre><div id="attributes" class="section"><h5><span class="secno">2.1.2.1 </span>Attributes</h5><dl class="attributes"><dt id="widl-MediaStreamOptions-audio"><code>audio</code> of type <span class="idlAttrType"><a>boolean</a></span></dt><dd>Set to false if an audio track is not required, default is true<div><em>No exceptions.</em></div></dd><dt id="widl-MediaStreamOptions-video"><code>video</code> of type <span class="idlAttrType"><a>boolean</a></span></dt><dd>Set to false if a video track is not required, default is true<div><em>No exceptions.</em></div></dd></dl></div>
  </div>

  <div id="navigatorusermediasuccesscallback" class="section">
  <h4><span class="secno">2.1.3 </span>NavigatorUserMediaSuccessCallback</h4>

  <pre class="idl"><span class="idlInterface" id="idl-def-NavigatorUserMediaSuccessCallback">[<span class="extAttr">Callback=FunctionOnly, NoInterfaceObject</span>]
interface <span class="idlInterfaceID">NavigatorUserMediaSuccessCallback</span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-NavigatorUserMediaSuccessCallback-handleEvent-void-LocalMediaStream-stream">handleEvent</a></span> (<span class="idlParam"><span class="idlParamType"><a href="#idl-def-LocalMediaStream" class="idlType"><code>LocalMediaStream</code></a></span> <span class="idlParamName">stream</span></span>);</span>
};</span>
</pre><div id="methods-1" class="section"><h5><span class="secno">2.1.3.1 </span>Methods</h5><dl class="methods"><dt id="widl-NavigatorUserMediaSuccessCallback-handleEvent-void-LocalMediaStream-stream"><code>handleEvent</code></dt><dd>(Explanation of handleEvent TBD)<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">stream</td><td class="prmType"><code><a href="#idl-def-LocalMediaStream" class="idlType"><code>LocalMediaStream</code></a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>
  </div>

  <div id="navigatorusermediaerror-and-navigatorusermediaerrorcallback" class="section">
  <h4><span class="secno">2.1.4 </span>NavigatorUserMediaError and NavigatorUserMediaErrorCallback</h4>

  <pre class="idl"><span class="idlInterface" id="idl-def-NavigatorUserMediaError">[<span class="extAttr">NoInterfaceObject</span>]
interface <span class="idlInterfaceID">NavigatorUserMediaError</span> {
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-NavigatorUserMediaError-PERMISSION_DENIED">PERMISSION_DENIED</a></span> = <span class="idlConstValue">1</span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>unsigned short</a></span> <span class="idlAttrName"><a href="#widl-NavigatorUserMediaError-code">code</a></span>;</span>
};</span>
</pre><div id="attributes-1" class="section"><h5><span class="secno">2.1.4.1 </span>Attributes</h5><dl class="attributes"><dt id="widl-NavigatorUserMediaError-code"><code>code</code> of type <span class="idlAttrType"><a>unsigned short</a></span>, readonly</dt><dd>Returns the current error's error code. At this time, this will always be 1, for
    which the constant <code title="dom-NavigatorUserMediaError-PERMISSION_DENIED"><a href="#widl-NavigatorUserMediaError-PERMISSION_DENIED">PERMISSION_DENIED</a></code> is
    defined.<div><em>No exceptions.</em></div></dd></dl></div><div id="constants" class="section"><h5><span class="secno">2.1.4.2 </span>Constants</h5><dl class="constants"><dt id="widl-NavigatorUserMediaError-PERMISSION_DENIED"><code>PERMISSION_DENIED</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The user denied the page permission to use the user's media devices.</dd></dl></div>

  <pre class="idl"><span class="idlInterface" id="idl-def-NavigatorUserMediaErrorCallback">[<span class="extAttr">Callback=FunctionOnly, NoInterfaceObject</span>]
interface <span class="idlInterfaceID">NavigatorUserMediaErrorCallback</span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-NavigatorUserMediaErrorCallback-handleEvent-void-NavigatorUserMediaError-error">handleEvent</a></span> (<span class="idlParam"><span class="idlParamType"><a href="#idl-def-NavigatorUserMediaError" class="idlType"><code>NavigatorUserMediaError</code></a></span> <span class="idlParamName">error</span></span>);</span>
};</span>
</pre><div id="methods-2" class="section"><h5><span class="secno">2.1.4.3 </span>Methods</h5><dl class="methods"><dt id="widl-NavigatorUserMediaErrorCallback-handleEvent-void-NavigatorUserMediaError-error"><code>handleEvent</code></dt><dd>(Explanation of handleEvent TBD)<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-NavigatorUserMediaError" class="idlType"><code>NavigatorUserMediaError</code></a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>
  </div>
  </div>

  <div id="examples" class="section">
  <h3><span class="secno">2.2 </span>Examples</h3>

  <div class="example">
    <p>A voice chat feature in a game could attempt to get access to the user's
    microphone by calling the API as follows:</p>
    <pre>&lt;script&gt;
 navigator.getUserMedia('audio', gotAudio);
 function gotAudio(stream) {
   // ... use 'stream' ...
 }
&lt;/script&gt;
</pre>
  </div>

  <div class="example">
    <p>A video-conferencing system would ask for both audio and video:</p>
    <pre>&lt;script&gt;
 function beginCall() {
   navigator.getUserMedia('audio,video user', gotStream);
 }
 function gotStream(stream) {
   // ... use 'stream' ...
 }
&lt;/script&gt;
</pre>
  </div>
  </div>
  </div>

  <div id="stream-api" class="section">
  
<!-- OddPage -->
<h2><span class="secno">3. </span>Stream API</h2>

  <div id="introduction" class="section">
  <h3><span class="secno">3.1 </span>Introduction</h3>

  <p>The <code><a href="#mediastream">MediaStream</a></code> interface is used to
  represent streams of media data, typically (but not necessarily) of audio and/or video
  content, e.g. from a local camera or a remote site. The data from a <code><a href="#mediastream">MediaStream</a></code> object does not necessarily have a canonical
  binary form; for example, it could just be &quot;the video currently coming from the user's
  video camera&quot;. This allows user agents to manipulate media streams in whatever fashion
  is most suitable on the user's platform.</p>

  <p>Each <code><a href="#mediastream">MediaStream</a></code> object can represent zero
  or more tracks, in particular audio and video tracks. Tracks can contain multiple
  channels of parallel data; for example a single audio track could have nine channels of
  audio data to represent a 7.2 surround sound audio track.</p>

  <p>Each track represented by a <code><a href="#mediastream">MediaStream</a></code>
  object has a corresponding <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> object.</p>

  <p>A <code><a href="#mediastream">MediaStream</a></code> object has an input and an
  output. The input depends on how the object was created: a <code><a href="#localmediastream">LocalMediaStream</a></code> object generated by a <code title="dom-navigator-getUserMedia"><a href="#widl-NavigatorUserMedia-getUserMedia-void-MediaStreamOptions-options-NavigatorUserMediaSuccessCallback-successCallback-NavigatorUserMediaErrorCallback-errorCallback">getUserMedia()</a></code> call, for instance, might take
  its input from the user's local camera, while a <code><a href="#mediastream">MediaStream</a></code> created by a <code><a href="#peerconnection">PeerConnection</a></code> object will take as input the data received
  from a remote peer. The output of the object controls how the object is used, e.g. what
  is saved if the object is written to a file, what is displayed if the object is used in
  a <code>video</code> element, or indeed what is transmitted to a remote peer if the
  object is used with a <code><a href="#peerconnection">PeerConnection</a></code>
  object.</p>

  <p>Each track in a <code><a href="#mediastream">MediaStream</a></code> object can be
  disabled, meaning that it is muted in the object's output. All tracks are initially
  enabled.</p>

  <p id="finishedMute">A <code><a href="#mediastream">MediaStream</a></code> can be
  <a href="#concept-stream-finished" title="concept-stream-finished">finished</a>,
  indicating that its inputs have forever stopped providing data. When a <code><a href="#mediastream">MediaStream</a></code> object is finished, all its tracks are muted
  regardless of whether they are enabled or disabled.</p>

  <p>The output of a <code><a href="#mediastream">MediaStream</a></code> object must
  correspond to the tracks in its input. Muted audio tracks must be replaced with
  silence. Muted video tracks must be replaced with blackness.</p>

  <p>A new <code><a href="#mediastream">MediaStream</a></code> object can be created
  from a list of <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> objects
  using the <code title="dom-MediaStream"><a href="#dom-mediastream">MediaStream()</a>
  </code> constructor. The list of <code><a href="#mediastreamtrack">MediaStreamTrack</a>
  </code> objects can be the track list of another stream, a subset of the track list of
  a stream or a composition of <code><a href="#mediastreamtrack">MediaStreamTrack</a>
  </code> objects from different <code><a href="#mediastream">MediaStream</a></code> objects.

  </p><p><img alt="" src="images/media-stream-1.png" /></p>
<!--  no alt since
  it's all described in the previous paragraphs: this is just a
  summary  -->

  
<!-- 
c.clearRect(0, 0, 640, 480);
c.save();
try {
  with (c) {
    save();
    strokeStyle = '#AA0000';
    lineWidth = 20;
    beginPath();
    moveTo(50,98);
    lineTo(550, 98);
    stroke();
  }
  mediaStream(c,50,10, true);

} finally {
  c.restore();
}

function cameraIcon(c,x,y) {
  with (c) { save(); try {
    translate(x,y);
    fillRect(-10,-10,20,20);
    beginPath();
    moveTo(7,0);
    lineTo(20,-10);
    lineTo(20,10);
    fill();
    font = '100 8px "Press Start 2P", sans-serif';
    textAlign = 'center';
    textBaseline = 'top';
    fillText('Camera', 4, 15);
  } finally { restore(); } }
}

function mediaStream(c,x,y,vid) {
  with (c) {
    save();
    translate(x-10,y-97);

    // cable
    fillStyle = 'black';
    font = '100 10px "Press Start 2P", sans-serif';
    textAlign = 'right';
    fillText('Input', 95, 170);
    textAlign = 'left';
    fillText('Output', 407, 170);

    // media stream
    fillStyle = '#EE8800';
    strokeStyle = '#FFCC00';
    lineWidth = 6;
    fillRect(100,100,300,170);
    strokeRect(100,100,300,170);
    fillStyle = 'black';
    font = '900 12px "Press Start 2P", sans-serif';
    textAlign = 'left';
    fillText('MediaStream', 110, 123);

    // tracks
    textAlign = 'left';
    strokeStyle = '#CC3300';
    fillStyle = '#FFFF00';
    lineWidth = 4;
    globalAlpha = vid ? 1 : 0.4;
    fillRect(120,140,100,110);
    strokeRect(120,140,100,110);
    globalAlpha = 1;
    fillRect(238,140,100,110);
    strokeRect(238,140,100,110);
    fillStyle = 'black';
    font = '900 10px "Press Start 2P", sans-serif';
    globalAlpha = vid ? 1 : 0.4;
    fillText('Track', 123, 155);
    fillText('(video)', 123, 170);
    globalAlpha = 1;
    fillText('Track', 241, 155);
    fillText('(stereo', 241, 170);
    fillText(' audio)', 241, 185);

    // channels
    strokeStyle = '#999999';
    fillStyle = '#FFFFFF';
    lineWidth = 2;
    fillRect(245,191,86,23);
    strokeRect(245,191,86,23);
    fillRect(245,220,86,23);
    strokeRect(245,220,86,23);
    fillStyle = 'black';
    font = '100 8px "Press Start 2P", sans-serif';
    textAlign = 'left';
    textBaseline = 'alphabetic';
    fillText('left', 249, 202);
    fillText('channel', 249, 211);
    fillText('right', 249, 231);
    fillText('channel', 249, 240);

    // track check marks
    fillStyle = 'black';
    font = '900 35px "Lucida Grande", sans-serif';
    textAlign = 'center';
    textBaseline = 'middle';
    fillText(vid ? '\u2713' : '\u2716', 220, 245);
    fillText('\u2713', 338, 245);

    restore();
  }
}
 -->


  <p>The ability to duplicate a <code><a href="#mediastream">MediaStream</a></code>, i.e.
  create a new <code><a href="#mediastream">MediaStream</a></code> object from the track
  list of an existing stream, allows for greater control since separate <code>
  <a href="#mediastream">MediaStream</a></code> instances can be manipulated and consumed
  individually. This can be used, for instance, in a video-conferencing scenario to display
  the local video from the user's camera and microphone in a local monitor, while only
  transmitting the audio to the remote peer (e.g. in response to the user using a &quot;video
  mute&quot; feature). Combining tracks from different <code><a href="#mediastream">MediaStream</a>
  </code> objects into a new <code><a href="#mediastream">MediaStream</a></code> makes it
  possible to, e.g., record selected tracks from a conversation involving several <code>
  <a href="#mediastream">MediaStream</a></code> objects with a single <code>
  <a href="#mediastreamrecorder">MediaStreamRecorder</a></code>.</p>

  
<!-- 
c.clearRect(0, 0, 640, 480);
c.save();
try {
  with (c) {
    save();
    strokeStyle = '#AA0000';
    lineWidth = 20;
    beginPath();
    moveTo(50,98);
    lineTo(550, 98);
    lineTo(550, 210);
    lineTo(50, 210);
    lineTo(50, 320);
    lineTo(550, 320);
    lineTo(550,420);
    stroke();
    beginPath();
    moveTo(50,320);
    lineTo(50,420);
    stroke();
    restore();
    fillStyle = 'black';
    font = '100 10px "Press Start 2P", sans-serif';
    textAlign = 'center';
    fillText('<video>', 50, 440);
    fillText('PeerConnection', 550, 440);
    font = '100 8px "Press Start 2P", sans-serif';
  }
  cameraIcon(c,25,98)
  mediaStream(c,50,10, true);
  mediaStream(c,50,233, false);

  with (c) {
    font = '100 8px "Press Start 2P", sans-serif';
    textAlign = 'left';
    textBaseline = 'middle';
    fillStyle = 'gray';

    fillText('from', 4, 130);
    fillText('getUserMedia()', 4, 140);

    fillText('via URL.getObjectURL()', 4, 450);

    textAlign = 'center';
    fillText('via addStream()', 550, 450);
  }
} finally {
  c.restore();
}

function cameraIcon(c,x,y) {
  with (c) { save(); try {
    translate(x,y);
    fillRect(-10,-10,20,20);
    beginPath();
    moveTo(7,0);
    lineTo(20,-10);
    lineTo(20,10);
    fill();
    font = '100 8px "Press Start 2P", sans-serif';
    textAlign = 'center';
    textBaseline = 'top';
    fillText('Camera', 4, 15);
  } finally { restore(); } }
}

function mediaStream(c,x,y,vid) {
  with (c) {
    save();
    translate(x-10,y-97);

    // cable
    fillStyle = 'black';
    font = '100 10px "Press Start 2P", sans-serif';
    textAlign = 'right';
    fillText('Input', 95, 170);
    textAlign = 'left';
    fillText('Output', 407, 170);

    // media stream
    fillStyle = '#EE8800';
    strokeStyle = '#FFCC00';
    lineWidth = 6;
    fillRect(100,100,300,170);
    strokeRect(100,100,300,170);
    fillStyle = 'black';
    font = '900 12px "Press Start 2P", sans-serif';
    textAlign = 'left';
    fillText(!vid ? 'MediaStream' : 'LocalMediaStream', 110, 123);

    // tracks
    textAlign = 'left';
    strokeStyle = '#CC3300';
    fillStyle = '#FFFF00';
    lineWidth = 4;
    globalAlpha = vid ? 1 : 0.4;
    fillRect(120,140,100,110);
    strokeRect(120,140,100,110);
    globalAlpha = 1;
    fillRect(238,140,100,110);
    strokeRect(238,140,100,110);
    fillStyle = 'black';
    font = '900 10px "Press Start 2P", sans-serif';
    globalAlpha = vid ? 1 : 0.4;
    fillText('Track', 123, 155);
    fillText('(video)', 123, 170);
    globalAlpha = 1;
    fillText('Track', 241, 155);
    fillText('(stereo', 241, 170);
    fillText(' audio)', 241, 185);

    // channels
    strokeStyle = '#999999';
    fillStyle = '#FFFFFF';
    lineWidth = 2;
    fillRect(245,191,86,23);
    strokeRect(245,191,86,23);
    fillRect(245,220,86,23);
    strokeRect(245,220,86,23);
    fillStyle = 'black';
    font = '100 8px "Press Start 2P", sans-serif';
    textAlign = 'left';
    textBaseline = 'alphabetic';
    fillText('left', 249, 202);
    fillText('channel', 249, 211);
    fillText('right', 249, 231);
    fillText('channel', 249, 240);

    // track check marks
    fillStyle = 'black';
    font = '900 35px "Lucida Grande", sans-serif';
    textAlign = 'center';
    textBaseline = 'middle';
    fillText(vid ? '\u2713' : '\u2716', 220, 245);
    fillText('\u2713', 338, 245);

    restore();
  }
}
 -->


  <p>The <code><a href="#localmediastream">LocalMediaStream</a></code> interface is used
  when the user agent is generating the stream's data (e.g. from a camera or streaming it
  from a local video file). It allows authors to control individual tracks during the
  generation of the content, e.g. to allow the user to temporarily disable a local camera
  during a video-conference chat.</p>

  <p>When a <code><a href="#localmediastream">LocalMediaStream</a></code> object is being
  generated from a local file (as opposed to a live audio/video source), the user agent
  should stream the data from the file in real time, not all at once. This reduces the
  ease with which pages can distinguish live video from pre-recorded video, which can
  help protect the user's privacy.</p>
  </div>
  <div id="interface-definitions" class="section">
  <h3><span class="secno">3.2 </span>Interface definitions</h3>

  <div id="mediastream" class="section">
  <h4><span class="secno">3.2.1 </span>MediaStream</h4>

  <p>The <dfn id="dom-mediastream" title="dom-MediaStream"><code>MediaStream(<var title="">trackList</var>)</code></dfn> constructor must return a new <code><a href="#mediastream">MediaStream</a></code> object with a newly generated label.
  A new <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> object is created
  for every unique underlying media source in <var title="">trackList</var> and appended
  to the new <code><a href="#mediastream">MediaStream</a></code> object's track list
  according to the track ordering constraints.

  </p><p>A <code><a href="#mediastream">MediaStream</a></code> object is said to <em>end</em>
  when the user agent learns that no more data will ever be forthcoming for this
  stream.</p>

  <p>When a <code><a href="#mediastream">MediaStream</a></code> object ends for any
  reason (e.g. because the user rescinds the permission for the page to use the local
  camera, or because the data comes from a finite file and the file's end has been
  reached and the user has not requested that it be looped, or because the stream comes
  from a remote peer and the remote peer has permanently stopped sending data, it is
  said to be <dfn id="concept-stream-finished" title="concept-stream-finished">finished
  </dfn>. When this happens for any reason other than the <code title="dom-MediaStream-stop">
  <a href="#dom-mediastream-stop">stop()</a></code> method being invoked, the user agent must
  queue a task that runs the following steps:</p>

  <ol>
    <li>
      <p>If the object's <code title="dom-MediaStream-readyState"><a href="#dom-mediastream-readystate">readyState</a></code> attribute has the value
      <code title="dom-MediaStream-ENDED"><a href="#widl-MediaStream-ENDED">ENDED</a></code> (2) already, then abort these steps. (The
      <code title="dom-MediaStream-stop"><a href="#dom-mediastream-stop">stop()</a></code> method was probably called just before
      the stream stopped for other reasons, e.g. the user clicked an in-page stop button
      and then the user-agent-provided stop button.)</p>
    </li>

    <li>
      <p>Set the object's <code title="dom-MediaStream-readyState"><a href="#dom-mediastream-readystate">readyState</a></code> attribute to <code title="dom-MediaStream-ENDED"><a href="#widl-MediaStream-ENDED">ENDED</a></code> (2).</p>
    </li>

    <li>
      <p>Fire a simple event named <code title="event-MediaStream-ended"><a href="#event-mediastream-ended">ended</a></code> at
      the object.</p>
    </li>
  </ol>

  <p>As soon as a <code><a href="#mediastream">MediaStream</a></code> object is <a href="#concept-stream-finished" title="concept-stream-finished">finished</a>, the stream's
  tracks start outputting only silence and/or blackness, as appropriate, <a href="#finishedMute">as defined earlier</a>.</p>

  <p>If the end of the stream was reached due to a user request, the task
  source for this <span title="concept-task">task</span> is the user
  interaction task source. Otherwise the task source for this
  <span title="concept-task">task</span> is the networking task source.</p>

  <pre class="idl"><span class="idlInterface" id="idl-def-MediaStream">[<span class="extAttr">Constructor (in MediaStreamTrackList trackList)</span>]
interface <span class="idlInterfaceID">MediaStream</span> {
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>DOMString</a></span>            <span class="idlAttrName"><a href="#widl-MediaStream-label">label</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a id="mediastreamtracklist">MediaStreamTrackList</a></span> <span class="idlAttrName"><a href="#widl-MediaStream-tracks">tracks</a></span>;</span>
<span class="idlMethod">    <span class="idlMethType"><a href="#idl-def-MediaStreamRecorder" class="idlType"><code>MediaStreamRecorder</code></a></span> <span class="idlMethName"><a href="#widl-MediaStream-record-MediaStreamRecorder">record</a></span> ();</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-MediaStream-LIVE">LIVE</a></span> = <span class="idlConstValue">1</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-MediaStream-ENDED">ENDED</a></span> = <span class="idlConstValue">2</span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>unsigned short</a></span>       <span class="idlAttrName"><a href="#widl-MediaStream-readyState">readyState</a></span>;</span>
<span class="idlAttribute">             attribute <span class="idlAttrType"><a>Function</a>?</span>            <span class="idlAttrName"><a href="#widl-MediaStream-onended">onended</a></span>;</span>
};</span>
</pre><div id="attributes-2" class="section"><h5><span class="secno">3.2.1.1 </span>Attributes</h5><dl class="attributes"><dt id="widl-MediaStream-label"><code>label</code> of type <span class="idlAttrType"><a>DOMString</a></span>, readonly</dt><dd>Returns a label that is unique to this stream, so that streams can be recognized
    after they are sent through the <code><a href="#peerconnection">PeerConnection</a></code> API.<div><em>No exceptions.</em></div></dd><dt id="widl-MediaStream-onended"><code>onended</code> of type <span class="idlAttrType"><a>Function</a></span>, nullable</dt><dd>This event handler, of type <code title="event-MediaStream-ended"><a href="#event-mediastream-ended">ended</a></code>, must be supported by all objects
    implementing the <code><a href="#mediastream">MediaStream</a></code> interface.<div><em>No exceptions.</em></div></dd><dt id="widl-MediaStream-readyState"><code>readyState</code> of type <span class="idlAttrType"><a>unsigned short</a></span>, readonly</dt><dd>
      <p>The <dfn id="dom-mediastream-readystate" title="dom-MediaStream-readyState"><code>readyState</code></dfn> attribute represents the
      state of the stream. It must return the value to which the user agent last set it
      (as defined below). It can have the following values: <dfn id="dfn-live">LIVE</dfn> or
      <dfn id="dfn-ended">ENDED</dfn>.</p>

      <p>When a <code><a href="#mediastream">MediaStream</a></code> object is created,
      its <code title="dom-MediaStream-readyState"><a href="#dom-mediastream-readystate">readyState</a></code> attribute must be set to
      <code title="dom-MediaStream-LIVE"><a href="#widl-MediaStream-LIVE">LIVE</a></code>
      (1), unless it is being created using the <code title="dom-MediaStream"><a href="#dom-mediastream">MediaStream()</a></code> constructor whose argument is a list of
      <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> objects whose underlying
      media sources will never produce any more data, in which case the <code><a href="#mediastream">MediaStream</a></code> object must be created with its <code title="dom-MediaStream-readyState"><a href="#dom-mediastream-readystate">readyState</a></code> attribute set to <code title="dom-MediaStream-ENDED"><a href="#widl-MediaStream-ENDED">ENDED</a></code> (2).</p>
    <div><em>No exceptions.</em></div></dd><dt id="widl-MediaStream-tracks"><code>tracks</code> of type <span class="idlAttrType"><a>MediaStreamTrackList</a></span>, readonly</dt><dd>
      <p>Returns a <code><a href="#mediastreamtracklist">MediaStreamTrackList</a></code>
      object representing the tracks that can be enabled and disabled.</p>

      <p>A <code><a href="#mediastream">MediaStream</a></code> can have multiple audio
      and video sources (e.g. because the user has multiple microphones, or because the
      real source of the stream is a media resource with
      many media tracks). The stream represented by a <code><a href="#mediastream">MediaStream</a></code> thus has zero or more tracks.</p>

      <p>The <dfn id="dom-mediastream-tracks" title="dom-MediaStream-tracks"><code>tracks</code></dfn> attribute must return an
      <span title="array host objects">array host object</span> for objects of type
      <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> that is <em>fixed
      length</em> and <em>read only</em>. The same object must be returned each time the
      attribute is accessed. [<cite><a class="bibref" rel="biblioentry" href="#bib-WEBIDL">WEBIDL</a></cite>]</p>

      <p>The array must contain the <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> objects that correspond to the the
      tracks of the stream. The relative order of all tracks in a user agent must be
      stable. All audio tracks must precede all video tracks. Tracks that come from a
      media resource whose format defines an order must be
      in the order defined by the format; tracks that come from a media resource whose format does not define an order must be
      in the relative order in which the tracks are declared in that media resource. Within these constraints, the order is
      user-agent defined.</p>
    <div><em>No exceptions.</em></div></dd></dl></div><div id="methods-3" class="section"><h5><span class="secno">3.2.1.2 </span>Methods</h5><dl class="methods"><dt id="widl-MediaStream-record-MediaStreamRecorder"><code>record</code></dt><dd>
      <p>Begins recording the stream. The returned <code><a href="#mediastreamrecorder">MediaStreamRecorder</a></code> object provides access to the
      recorded data.</p>

      <p>When the <dfn id="dom-mediastream-record" title="dom-MediaStream-record"><code>record()</code></dfn> method is invoked, the user
      agent must return a new <code><a href="#mediastreamrecorder">MediaStreamRecorder</a></code> object associated with the
      stream.</p>
    <div><em>No parameters.</em></div><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a href="#idl-def-MediaStreamRecorder" class="idlType"><code>MediaStreamRecorder</code></a></code></div></dd></dl></div><div id="constants-1" class="section"><h5><span class="secno">3.2.1.3 </span>Constants</h5><dl class="constants"><dt id="widl-MediaStream-ENDED"><code>ENDED</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The stream has finished (the user agent is no longer receiving or generating
    data, and will never receive or generate more data for this stream).</dd><dt id="widl-MediaStream-LIVE"><code>LIVE</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The stream is active (the user agent is making a best-effort attempt to receive
    or generate data in real time).</dd></dl></div>

  <pre class="idl"><span class="idlImplements"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a> implements <a>EventTarget</a>;</span></pre><div class="idlImplementsDesc"><p>All instances of the <code><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></code> type are defined to also implement the <a>EventTarget</a> interface.</p></div>
  </div>

  <div id="localmediastream" class="section">
  <h4><span class="secno">3.2.2 </span>LocalMediaStream</h4>

  <pre class="idl"><span class="idlInterface" id="idl-def-LocalMediaStream">interface <span class="idlInterfaceID">LocalMediaStream</span> : <span class="idlSuperclass"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-LocalMediaStream-stop-void">stop</a></span> ();</span>
};</span>
</pre><div id="methods-4" class="section"><h5><span class="secno">3.2.2.1 </span>Methods</h5><dl class="methods"><dt id="widl-LocalMediaStream-stop-void"><code>stop</code></dt><dd>
      <p>When a <code><a href="#localmediastream">LocalMediaStream</a></code> object's
      <dfn id="dom-mediastream-stop" title="dom-MediaStream-stop"><code>stop()</code></dfn> method is invoked, the user agent
      must queue a task that runs the following steps:</p>

      <ol>
        <li>
          <p>If the object's <code title="dom-MediaStream-readyState"><a href="#dom-mediastream-readystate">readyState</a></code> attribute is in the
          <code title="dom-MediaStream-ENDED"><a href="#widl-MediaStream-ENDED">ENDED</a></code> (2) state, then abort these
          steps.</p>
        </li>

        <li>
          <p>Permanently stop the generation of data for the stream. If the data is being
          generated from a live source (e.g. a microphone or camera), and no other stream
          is being generated from a live source, then the user agent should remove any
          active &quot;on-air&quot; indicator. If the data is being generated from a prerecorded
          source (e.g. a video file), any remaining content in the file is ignored. The
          stream is <a href="#concept-stream-finished" title="concept-stream-finished">finished</a>. The stream's tracks start outputting
          only silence and/or blackness, as appropriate, <a href="#finishedMute">as
          defined earlier</a>.</p>
        </li>

        <li>
          <p>Set the object's <code title="dom-MediaStream-readyState"><a href="#dom-mediastream-readystate">readyState</a></code> attribute to <code title="dom-MediaStream-ENDED"><a href="#widl-MediaStream-ENDED">ENDED</a></code>
          (2).</p>
        </li>

        <li>
          <p>Fire a simple event named <code title="event-MediaStream-ended"><a href="#event-mediastream-ended">ended</a></code>
          at the object.</p>
        </li>
      </ol>

      <p>The task source for the <span title="concept-task">tasks</span>
      queued for the <code title="dom-MediaStream-stop"><a href="#dom-mediastream-stop">stop()</a></code> method is the DOM manipulation task
      source.</p>
    <div><em>No parameters.</em></div><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>
  </div>

  <div id="mediastreamtrack" class="section">
  <h4><span class="secno">3.2.3 </span>MediaStreamTrack</h4>

  <pre class="idl"><span class="idlTypedef" id="idl-def-MediaStreamTrackList">typedef <span class="idlTypedefType"><a href="#idl-def-MediaStreamTrack" class="idlType"><code>MediaStreamTrack</code></a></span>[] <span class="idlTypedefID">MediaStreamTrackList</span>;</span></pre><div class="idlTypedefDesc">Throughout this specification, the identifier <span class="idlTypedefID">MediaStreamTrackList</span> is used to refer to the array of <span class="idlTypedefType"><a href="#idl-def-MediaStreamTrack" class="idlType"><code>MediaStreamTrack</code></a></span> type.</div>

  <pre class="idl"><span class="idlInterface" id="idl-def-MediaStreamTrack">interface <span class="idlInterfaceID">MediaStreamTrack</span> {
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>DOMString</a></span> <span class="idlAttrName"><a href="#widl-MediaStreamTrack-kind">kind</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>DOMString</a></span> <span class="idlAttrName"><a href="#widl-MediaStreamTrack-label">label</a></span>;</span>
<span class="idlAttribute">             attribute <span class="idlAttrType"><a>boolean</a></span>   <span class="idlAttrName"><a href="#widl-MediaStreamTrack-enabled">enabled</a></span>;</span>
};</span>
</pre><div id="attributes-3" class="section"><h5><span class="secno">3.2.3.1 </span>Attributes</h5><dl class="attributes"><dt id="widl-MediaStreamTrack-enabled"><code>enabled</code> of type <span class="idlAttrType"><a>boolean</a></span></dt><dd>
      <p>The <dfn id="dom-mediastreamtrack-enabled" title="dom-MediaStreamTrack-enabled"><code>MediaStreamTrack.enabled</code></dfn>
      attribute, on getting, must return the last value to which it was set. On setting,
      it must be set to the new value, and then, if the <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> object is still associated with a
      track, must enable the track if the new value is true, and disable it
      otherwise.</p>

      <p class="note">Thus, after a <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> is disassociated from its track,
      its <code title="dom-MediaStreamTrack-enabled"><a href="#dom-mediastreamtrack-enabled">enabled</a></code> attribute still changes value
      when set, it just doesn't do anything with that new value.</p>
    <div><em>No exceptions.</em></div></dd><dt id="widl-MediaStreamTrack-kind"><code>kind</code> of type <span class="idlAttrType"><a>DOMString</a></span>, readonly</dt><dd>
      <p>The <dfn id="dom-mediastreamtrack-kind" title="dom-MediaStreamTrack-kind"><code>MediaStreamTrack.kind</code></dfn> attribute must
      return the string &quot;<code title="&quot;&quot;">audio</code>&quot; if the object's corresponding
      track is or was an audio track, &quot;<code title="&quot;&quot;">video</code>&quot; if the
      corresponding track is or was a video track, and a user-agent defined string
      otherwise.</p>
    <div><em>No exceptions.</em></div></dd><dt id="widl-MediaStreamTrack-label"><code>label</code> of type <span class="idlAttrType"><a>DOMString</a></span>, readonly</dt><dd>
      <p>When a <code><a href="#localmediastream">LocalMediaStream</a></code> object is
      created, the user agent must generate a globally unique identifier string, and must
      initialize the object's <code title="dom-MediaStream-label"><a href="#dom-mediastream-label">label</a></code> attribute to that string. Such strings
      must only use characters in the ranges U+0021, U+0023 to U+0027, U+002A to U+002B,
      U+002D to U+002E, U+0030 to U+0039, U+0041 to U+005A, U+005E to U+007E, and must be
      36 characters long.</p>
<!--  UUIDs have 36 characters
  including hyphens; the ranges above comes from RFC4574 (the a=label:
  thing in SDP)  -->


      <p>When a <code><a href="#mediastream">MediaStream</a></code> is created to
      represent a stream obtained from a remote peer, the <code title="dom-MediaStream-label"><a href="#dom-mediastream-label">label</a></code> attribute
      is initialized from information provided by the remote source.</p>
      
<!--  described below
   -->


      <p>When a <code><a href="#mediastream">MediaStream</a></code> is created from
      another using the <code title="dom-MediaStream"><a href="#dom-mediastream">MediaStream()</a></code> constructor, the <code title="dom-MediaStream-label"><a href="#dom-mediastream-label">label</a></code> attribute
      is initialized to a newly generated value.</p>
<!--  described above  -->


      <p>The <dfn id="dom-mediastream-label" title="dom-MediaStream-label"><code>label</code></dfn> attribute must return the value to
      which it was initialized when the object was created.</p>

      <p class="note">The label of a <code><a href="#mediastream">MediaStream</a></code>
      object is unique to the source of the stream, but that does not mean it is not
      possible to end up with duplicates. For example, a locally
      generated stream could be sent from one user to a remote peer using <code><a href="#peerconnection">PeerConnection</a></code>, and then sent back to the original
      user in the same manner, in which case the original user will have multiple streams
      with the same label (the locally-generated one and the one received from the remote
      peer).</p>

      <p>User agents may label audio and video sources (e.g. &quot;Internal microphone&quot; or
      &quot;External USB Webcam&quot;). The <dfn id="dom-mediastreamtrack-label" title="dom-MediaStreamTrack-label"><code>MediaStreamTrack.label</code></dfn> attribute
      must return the label of the object's corresponding track, if any. If the
      corresponding track has or had no label, the attribute must instead return the
      empty string.</p>

      <p class="note">Thus the <code title="dom-MediaStreamTrack-kind"><a href="#dom-mediastreamtrack-kind">kind</a></code> and <code title="dom-MediaStreamTrack-label"><a href="#dom-mediastreamtrack-label">label</a></code>
      attributes do not change value, even if the <code><a href="#mediastreamtrack">MediaStreamTrack</a></code> object is disassociated from its
      corresponding track.</p>
    <div><em>No exceptions.</em></div></dd></dl></div>
  </div>

  <div id="mediastreamrecorder" class="section">
  <h4><span class="secno">3.2.4 </span>MediaStreamRecorder</h4>

  <pre class="idl"><span class="idlInterface" id="idl-def-MediaStreamRecorder">interface <span class="idlInterfaceID">MediaStreamRecorder</span> {
<span class="idlMethod">    <span class="idlMethType"><a>voice</a></span> <span class="idlMethName"><a href="#widl-MediaStreamRecorder-getRecordedData-voice-BlobCallback-callback">getRecordedData</a></span> (<span class="idlParam"><span class="idlParamType"><a href="#idl-def-BlobCallback" class="idlType"><code>BlobCallback</code></a>?</span> <span class="idlParamName">callback</span></span>);</span>
};</span>
</pre><div id="methods-5" class="section"><h5><span class="secno">3.2.4.1 </span>Methods</h5><dl class="methods"><dt id="widl-MediaStreamRecorder-getRecordedData-voice-BlobCallback-callback"><code>getRecordedData</code></dt><dd>
      <p>Creates a <code>Blob</code> of the recorded data, and invokes the provided
      callback with that <code>Blob</code>.</p>

      <p>When the <dfn id="dom-mediastreamrecorder-getrecordeddata" title="dom-MediaStreamRecorder-getRecordedData"><code>getRecordedData()</code></dfn>
      method is called, the user agent must run the following steps:</p>

      <ol>
        <li>
          <p>Let <var title="">callback</var> be the callback indicated by the method's
          first argument.</p>
        </li>

        <li>
          <p>If <var title="">callback</var> is null, abort these steps.</p>
        </li>
<!--  we could throw an exception instead (that's
   why the method doesn't return until later: so that we can add an
   exception here without changing the algorithm)  -->


        <li>
          <p>Let <var title="">data</var> be the data that was streamed by the
          <code><a href="#mediastream">MediaStream</a></code> object from which the
          <code><a href="#mediastreamrecorder">MediaStreamRecorder</a></code> was created
          since the creation of the <code><a href="#mediastreamrecorder">MediaStreamRecorder</a></code> object.</p>
        </li>

        <li>
          <p>Return, and run the remaining steps asynchronously.</p>
        </li>

        <li>
          <p>Generate a file that containing <var title="">data</var> in a format
          supported by the user agent for use in <code>audio</code> and
          <code>video</code> elements.</p>
        </li>

        <li>
          <p>Let <var title="">blob</var> be a <code>Blob</code> object representing the
          contents of the file generated in the previous step. [<cite><a class="bibref" rel="biblioentry" href="#bib-FILE-API">FILE-API</a></cite>]</p>
        </li>

        <li>
          <p>Queue a task to invoke <var title="">callback</var> with
          <var title="">blob</var> as its argument.</p>
        </li>
      </ol>

      <p class="note">The <code title="dom-MediaStreamRecorder-getRecordedData"><a href="#dom-mediastreamrecorder-getrecordeddata">getRecordedData()</a></code> method can
      be called multiple times on one <code><a href="#mediastreamrecorder">MediaStreamRecorder</a></code> object; each time, it will
      create a new file as if this was the first time the method was being called. In
      particular, the method does not stop or reset the recording when the method is
      called.</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">callback</td><td class="prmType"><code><a href="#idl-def-BlobCallback" class="idlType"><code>BlobCallback</code></a></code></td><td class="prmNullTrue">✔</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>voice</a></code></div></dd></dl></div>
  </div>

  <div id="blobcallback" class="section">
  <h4><span class="secno">3.2.5 </span>BlobCallback</h4>

  <pre class="idl"><span class="idlInterface" id="idl-def-BlobCallback">[<span class="extAttr">Callback=FunctionOnly, NoInterfaceObject</span>]
interface <span class="idlInterfaceID">BlobCallback</span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-BlobCallback-handleEvent-void-Blob-blob">handleEvent</a></span> (<span class="idlParam"><span class="idlParamType"><a>Blob</a></span> <span class="idlParamName">blob</span></span>);</span>
};</span>
</pre><div id="methods-6" class="section"><h5><span class="secno">3.2.5.1 </span>Methods</h5><dl class="methods"><dt id="widl-BlobCallback-handleEvent-void-Blob-blob"><code>handleEvent</code></dt><dd>Def TBD<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">blob</td><td class="prmType"><code><a>Blob</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>
  </div>

  <div id="url" class="section">
  <h4><span class="secno">3.2.6 </span>URL</h4>

  <p><em>Note that the following is actually only a partial interface, but ReSpec does
  not yet support that.</em></p>

  <pre class="idl"><span class="idlInterface" id="idl-def-URL">interface <span class="idlInterfaceID">URL</span> {
<span class="idlMethod">    <span class="idlMethType"><a>static DOMString</a></span> <span class="idlMethName"><a href="#widl-URL-createObjectURL-static-DOMString-MediaStream-stream">createObjectURL</a></span> (<span class="idlParam"><span class="idlParamType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></span> <span class="idlParamName">stream</span></span>);</span>
};</span>
</pre><div id="methods-7" class="section"><h5><span class="secno">3.2.6.1 </span>Methods</h5><dl class="methods"><dt id="widl-URL-createObjectURL-static-DOMString-MediaStream-stream"><code>createObjectURL</code></dt><dd>
      <p>Mints a <a href="#blob-url">Blob URL</a> to refer to the given <code><a href="#mediastream">MediaStream</a></code>.</p>

      <p>When the <dfn id="dom-url-createobjecturl" title="dom-URL-createObjectURL"><code>createObjectURL()</code></dfn> method is called
      with a <code><a href="#mediastream">MediaStream</a></code> argument, the user agent
      must return a unique <a href="#blob-url">Blob URL</a> for the given <code><a href="#mediastream">MediaStream</a></code>. [<cite><a class="bibref" rel="biblioentry" href="#bib-FILE-API">FILE-API</a></cite>]</p>

      <p>For audio and video streams, the data exposed on that stream must be in a format
      supported by the user agent for use in <code>audio</code> and <code>video</code>
      elements.</p>

      <p class="bookkeeping">A <dfn id="blob-url">Blob URL</dfn> is the same as what the
      File API specification calls a Blob URI, except that anything in the
      definition of that feature that refers to <code>File</code> and <code>Blob</code>
      objects is hereby extended to also apply to <code><a href="#mediastream">MediaStream</a></code> and <code><a href="#localmediastream">LocalMediaStream</a></code> objects.</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">stream</td><td class="prmType"><code><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>static DOMString</a></code></div></dd></dl></div>
  </div>
  </div>

  <div id="examples-1" class="section">
  <h3><span class="secno">3.3 </span>Examples</h3>

  <div class="example">
    <p>This sample code exposes a button. When clicked, the button is disabled and the
    user is prompted to offer a stream. The user can cause the button to be re-enabled by
    providing a stream (e.g. giving the page access to the local camera) and then
    disabling the stream (e.g. revoking that access).</p>
    <pre>&lt;input type=&quot;button&quot; value=&quot;Start&quot; onclick=&quot;start()&quot; id=&quot;startBtn&quot;&gt;
&lt;script&gt;
 var startBtn = document.getElementById('startBtn');
 function start() {
   navigator.getUserMedia('audio,video', gotStream);
   startBtn.disabled = true;
 }
 function gotStream(stream) {
   stream.onended = function () {
     startBtn.disabled = false;
   }
 }
&lt;/script&gt;
</pre>
  </div>

  <div class="example">
    <p>This example allows people to record a short audio message and upload it to the
    server. This example even shows rudimentary error handling.</p>
    <pre>&lt;input type=&quot;button&quot; value=&quot;⚫&quot; onclick=&quot;msgRecord()&quot; id=&quot;recBtn&quot;&gt;
&lt;input type=&quot;button&quot; value=&quot;◼&quot; onclick=&quot;msgStop()&quot; id=&quot;stopBtn&quot; disabled&gt;
&lt;p id=&quot;status&quot;&gt;To start recording, press the ⚫ button.&lt;/p&gt;
&lt;script&gt;
 var recBtn = document.getElementById('recBtn');
 var stopBtn = document.getElementById('stopBtn');
 function report(s) {
   document.getElementById('status').textContent = s;
 }
 function msgRecord() {
   report('Attempting to access microphone...');
   navigator.getUserMedia('audio', gotStream, noStream);
   recBtn.disabled = true;
 }
 var msgStream, msgStreamRecorder;
 function gotStream(stream) {
   report('Recording... To stop, press to ◼ button.');
   msgStream = stream;
   msgStreamRecorder = stream.record();
   stopBtn.disabled = false;
   stream.onended = function () {
     msgStop();     
   }
 }
 function msgStop() {
   report('Creating file...');
   stopBtn.disabled = true;
   msgStream.onended = null;
   msgStream.stop();
   msgStreamRecorder.getRecordedData(msgSave);
 }
 function msgSave(blob) {
   report('Uploading file...');
   var x = new XMLHttpRequest();
   x.open('POST', 'uploadMessage');
   x.send(blob);
   x.onload = function () {
     report('Done! To record a new message, press the ⚫ button.');
     recBtn.disabled = false;
   };
   x.onerror = function () {
     report('Failed to upload message. To try recording a message again, press the ⚫ button.');
     recBtn.disabled = false;
   };
 }
 function noStream() {
   report('Could not obtain access to your microphone. To try again, press the ⚫ button.');
   recBtn.disabled = false;
 }
&lt;/script&gt;
</pre>
  </div>

  <div class="example">
    <p>This example allows people to take photos of themselves from the local video
    camera.</p>
    <pre>&lt;article&gt;
 &lt;style scoped&gt;
  video { transform: scaleX(-1); }
  p { text-align: center; }
 &lt;/style&gt;
 &lt;h1&gt;Snapshot Kiosk&lt;/h1&gt;
 &lt;section id=&quot;splash&quot;&gt;
  &lt;p id=&quot;errorMessage&quot;&gt;Loading...&lt;/p&gt;
 &lt;/section&gt;
 &lt;section id=&quot;app&quot; hidden&gt;
  &lt;p&gt;&lt;video id=&quot;monitor&quot; autoplay&gt;&lt;/video&gt; &lt;canvas id=&quot;photo&quot;&gt;&lt;/canvas&gt;
  &lt;p&gt;&lt;input type=button value=&quot;&amp;#x1F4F7;&quot; onclick=&quot;snapshot()&quot;&gt;
 &lt;/section&gt;
 &lt;script&gt;
  navigator.getUserMedia('video user', gotStream, noStream);
  var video = document.getElementById('monitor');
  var canvas = document.getElementById('photo');
  function gotStream(stream) {
    video.src = URL.getObjectURL(stream);
    video.onerror = function () {
      stream.stop();
    };
    stream.onended = noStream;
    video.onloadedmetadata = function () {
      canvas.width = video.videoWidth;
      canvas.height = video.videoHeight;
      document.getElementById('splash').hidden = true;
      document.getElementById('app').hidden = false;
    };
  }
  function noStream() {
    document.getElementById('errorMessage').textContent = 'No camera available.';
  }
  function snapshot() {
    canvas.getContext('2d').drawImage(video, 0, 0);
  }
 &lt;/script&gt;
&lt;/article&gt;
</pre>
  </div>
  </div>
  </div>

  <div id="peer-to-peer-connections" class="section">
  
<!-- OddPage -->
<h2><span class="secno">4. </span>Peer-to-peer connections</h2>

  <p>A <code><a href="#peerconnection">PeerConnection</a></code> allows two users to
  communicate directly, browser-to-browser. Communications are coordinated via a
  signaling channel provided by script in the page via the server, e.g. using
  <code>XMLHttpRequest</code>.</p>

  <p>Calling &quot;new <code title="dom-PeerConnection"><a href="#dom-peerconnection">PeerConnection</a></code>(<var title="">configuration</var>,
  <var title="">signalingCallback</var>)&quot; creates a <code><a href="#peerconnection">PeerConnection</a></code> object.</p>

  <p>The <var title="">configuration</var> string gives the address of a STUN or TURN
  server to use to establish the connection. [<cite><a class="bibref" rel="biblioentry" href="#bib-STUN">STUN</a></cite>] [<cite><a class="bibref" rel="biblioentry" href="#bib-TURN">TURN</a></cite>]</p>

  <p>The allowed formats for this string are:</p>

  <dl>
    <dt>&quot;<code title="&quot;&quot;"><var title="">TYPE</var> 203.0.113.2:3478</code>&quot;</dt>

    <dd>
      <p>Indicates a specific IP address and port for the server.</p>
    </dd>

    <dt>&quot;<code title="&quot;&quot;"><var title="">TYPE</var> relay.example.net:3478</code>&quot;&quot;</dt>

    <dd>
      <p>Indicates a specific host and port for the server; the user agent will look up
      the IP address in DNS.</p>
    </dd>

    <dt>&quot;<code title="&quot;&quot;"><var title="">TYPE</var> example.net</code>&quot;&quot;</dt>

    <dd>
      <p>Indicates a specific domain for the server; the user agent will look up the IP
      address and port in DNS.</p>
    </dd>
  </dl>

  <p>The &quot;<code title="&quot;&quot;"><var title="">TYPE</var></code>&quot; is one of:</p>

  <dl>
    <dt><code title="&quot;&quot;">STUN</code></dt>

    <dd>Indicates a STUN server</dd>

    <dt><code title="&quot;&quot;">STUNS</code></dt>

    <dd>Indicates a STUN server that is to be contacted using a TLS session.</dd>

    <dt><code title="&quot;&quot;">TURN</code></dt>

    <dd>Indicates a TURN server</dd>

    <dt><code title="&quot;&quot;">TURNS</code></dt>

    <dd>Indicates a TURN server that is to be contacted using a TLS session.</dd>
  </dl>

  <p>The <var title="">signalingCallback</var> argument is a method that will be invoked
  when the user agent needs to send a message to the other host over the signaling
  channel. When the callback is invoked, convey its first argument (a string) to the
  other peer using whatever method is being used by the Web application to relay
  signaling messages. (Messages returned from the other peer are provided back to the
  user agent using the <code title="dom-PeerConnection-processSignalingMessage"><a href="#dom-peerconnection-processsignalingmessage">processSignalingMessage()</a></code>
  method.)</p>

  <p>A <code><a href="#peerconnection">PeerConnection</a></code> object has an associated
  <dfn id="peerconnection-signaling-callback"><code>PeerConnection</code> signaling
  callback</dfn>, a <dfn id="peerconnection-ice-agent"><code>PeerConnection</code> ICE
  Agent</dfn>,
  
  a <dfn id="peerconnection-readiness-state"><code>PeerConnection</code>
  readiness state</dfn> and an <dfn id="ice-started-flag">SDP Agent</dfn>. These
  are initialized when the object is created.</p>

  <p>When the <dfn id="dom-peerconnection" title="dom-PeerConnection"><code>PeerConnection()</code></dfn> constructor is invoked, the
  user agent must run the following steps. This algorithm has a synchronous
  section (which is triggered as part of the event loop algorithm).
  Steps in the synchronous section are marked with ⌛.</p>

  <ol>
    <li>
      <p>Let <var title="">serverConfiguration</var> be the constructor's first
      argument.</p>
    </li>

    <li>
      <p>Let <var title="">signalingCallback</var> be the constructor's second
      argument.</p>
    </li>

    <li>
      <p>Let <var title="">connection</var> be a newly created <code><a href="#peerconnection">PeerConnection</a></code> object.</p>
    </li>

    <li>
      <p>Create an ICE Agent and let <var title="">connection</var>'s <a href="#peerconnection-ice-agent"><code>PeerConnection</code> ICE Agent</a> be that ICE
      Agent. [<cite><a class="bibref" rel="biblioentry" href="#bib-ICE">ICE</a></cite>]</p>
    </li>

    <li>
      <p>If <var title="">serverConfiguration</var> contains a U+000A LINE FEED (LF)
      character or a U+000D CARRIAGE RETURN (CR) character (or both), remove all
      characters from <var title="">serverConfiguration</var> after the first such
      character.</p>
    </li>

    <li>
      <p><span title="split a string on spaces">Split <var title="">serverConfiguration</var> on spaces</span> to obtain <var title="">configuration
      components</var>.</p>
    </li>

    <li>
      <p>If <var title="">configuration components</var> has two or more components, and
      the first component is a case-sensitive match for one of the following
      strings:</p>

      <ul class="breif">
        <li>&quot;<code title="">STUN</code>&quot;</li>

        <li>&quot;<code title="">STUNS</code>&quot;</li>

        <li>&quot;<code title="">TURN</code>&quot;</li>

        <li>&quot;<code title="">TURNS</code>&quot;</li>
      </ul>

      <p>...then run the following substeps:</p>

      <ol>
        <li>
          <p>Let <var title="">server type</var> be STUN if the first component of
          <var title="">configuration components</var> is '<code title="">STUN</code>' or
          '<code title="">STUNS</code>', and TURN otherwise (the first component of
          <var title="">configuration components</var> is &quot;<code title="">TURN</code>&quot; or
          &quot;<code title="">TURNS</code>&quot;).</p>
        </li>

        <li>
          <p>Let <var title="">secure</var> be true if the first component of <var title="">configuration components</var> is &quot;<code title="">STUNS</code>&quot; or
          &quot;<code title="">TURNS</code>&quot;, and false otherwise.</p>
        </li>

        <li>
          <p>Let <var title="">host</var> be the contents of the second component of
          <var title="">configuration components</var> up to the character before the
          first U+003A COLON character (:), if any, or the entire string otherwise.</p>
        </li>

        <li>
          <p>Let <var title="">port</var> be the contents of the second component of
          <var title="">configuration components</var> from the character after the first
          U+003A COLON character (:) up to the end, if any, or the empty string
          otherwise.</p>
        </li>

        <li>
          <p>Configure the <a href="#peerconnection-ice-agent"><code>PeerConnection</code> ICE Agent</a>'s STUN or
          TURN server as follows:</p>

          <ul>
            <li>If <var title="">server type</var> is STUN, the server is a STUN server.
            Otherwise, <var title="">server type</var> is TURN and the server is a TURN
            server.</li>

            <li>If <var title="">secure</var> is true, the server is to be contacted
            using TLS-over-TCP, otherwise, it is to be contacted using UDP.</li>

            <li>The IP address, host name, or domain name of the server is <var title="">host</var>.</li>

            <li>The port to use is <var title="">port</var>. If this is the empty string,
            then only a domain name is configured (and the ICE Agent will use DNS SRV
            requests to determine the IP address and port).</li>

            <li>The long-term username for the STUN or TURN server is the <span title="ASCII serialization of an origin">ASCII serialization</span> of the
            entry script's origin; the long-term password is
            the empty string.</li>
          </ul>

          <p>If the given IP address, host name, domain name, or port are invalid, then
          the user agent must act as if no STUN or TURN server is configured.</p>
        </li>
      </ol>
    </li>

    <li>
      <p>Let the <var title="">connection</var>'s <a href="#peerconnection-signaling-callback"><code>PeerConnection</code> signaling
      callback</a> be <var title="">signalingCallback</var>.</p>
    </li>

    <li>
      <p>Set <var title="">connection</var>'s <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness state</a>
      to <code title="dom-PeerConnection-NEW"><a href="#widl-PeerConnection-NEW">NEW</a></code> (0).</p>
    </li>

    <li>
     <p>Set <var title="">connection</var>'s <a href="#peerconnection-readiness-state"><code>PeerConnection</code> ice state </a>
      to <code title="dom-PeerConnection-NEW"><a href="#widl-PeerConnection-NEW">NEW</a></code> (0).</p>
    </li>

        <li>
     <p>Set <var title="">connection</var>'s <a href="#peerconnection-readiness-state"><code>PeerConnection</code> sdp state </a>
      to <code title="dom-PeerConnection-NEW"><a href="#widl-PeerConnection-NEW">NEW</a></code> (0).</p>
    </li>
    
    <li>
      <p>Let <var title="">connection</var>'s <code title="dom-PeerConnection-localStreams"><a href="#widl-PeerConnection-localStreams">localStreams</a></code> attribute be an empty
      read-only <code><a href="#mediastream">MediaStream</a></code> array.
      [<cite><a class="bibref" rel="biblioentry" href="#bib-WEBIDL">WEBIDL</a></cite>]</p>
    </li>

    <li>
      <p>Let <var title="">connection</var>'s <code title="dom-PeerConnection-remoteStreams"><a href="#widl-PeerConnection-remoteStreams">remoteStreams</a></code> attribute be an empty
      read-only <code><a href="#mediastream">MediaStream</a></code> array.
      [<cite><a class="bibref" rel="biblioentry" href="#bib-WEBIDL">WEBIDL</a></cite>]</p>
    </li>

    <li>
      <p>Return <var title="">connection</var>, but continue these steps
      asynchronously.</p>
    </li>

    <li>
      <p>Await a stable state. The synchronous section consists
      of the remaining steps of this algorithm. (Steps in <span title="synchronous section">synchronous sections</span> are marked with ⌛.)</p>
    </li>

    <li> <p>⌛ If the ice state is set to NEW, it must queue a task to start
    gathering ICE address and set the ice state to ICEGATHERING.</p> </li>
    
    <li> <p>⌛ Once the ICE address gathering is complete, if there are any streams in
    localStreams, the SDP Agent will send the initial the SDP offer. The 
    initial SDP offer <em class="rfc2119" title="must">must</em> contain both the ICE candidate information
    as well as the SDP to represent the media descriptions for all the
    streams in localStreams. </p> </li>
    
 </ol>

  <p> During the lifetime of the peerConnection object, the following
     procedures are followed: </p>

  <ol>
     <li> <p> If a local media stream has been added and an SDP offer needs to
    be sent, and the ICE state is not NEW or ICEGATHERING, and the SDP Agent
    state is NEW or SDPIDLE, then send and queue a task to send an SDP offer and
    change the SPD state to SDP Waiting.</p> </li>

    <li> <p> If an SDP offer has been received, and the SDP state is NEW or
    SDPIDLE, pass the ICE candidates from the SDP offer to the ICE Agent and
    change it state to ICECHECKING. Construct an appropriate SDP answer, update the
    remote streams, queue a task to send the SDP offer, and set the SDPAgent
    state to SDPIDLE. </p> </li>

    <li> <p> At the point the sdpState changes from NEW to some other
    state, the readyState changes to NEGOTIATING.  </p> </li>

     <li> <p> If the ICE Agent finds a candidates that froms a valid
    connection, the ICE state is changed to ICECONNECTED </p> </li>

     <li> <p> If the ICE Agent finishes checking all candidates, if a
    connection has been found, the ice state is changed to ICECOMPLETED and if
    not connection has been found it is changed to ICEFAILED. </p> </li>

     <li> <p> If the iceState is ICECONNECTED or ICECOMPLETED and the
   SDP stat is SDPIDLE, the readyState is set to ACTIVE. </p> </li>
   
    <li> <p> If the iceState is ICEFAILED, a task is queued to calls the close method. </p> </li>
  
    <li> <p> The close method will cause the system to wait until the sdpStat
    is SDPIDLE then it will send an SDP offer terminating all media and change
    the readyState to CLOSING as well as stop all ICE process and change the
    iceState to ICE_CLOSED. Once an SDP anser to this offer is received, the
    readyState will be changed to CLOSED.  </p> </li>
  
</ol>
    
  <p>User agents may negotiate any codec and any resolution, bitrate, or other quality
  metric. User agents are encouraged to initially negotiate for the native resolution of
  the stream. For streams that are then rendered (using a <code>video</code> element),
  user agents are encouraged to renegotiate for a resolution that matches the rendered
  display size.</p>

  <p class="note">Starting with the native resolution means that if the Web application
  notifies its peer of the native resolution as it starts sending data, and the peer
  prepares its <code>video</code> element accordingly, there will be no need for a
  renegotiation once the stream is flowing.</p>

  <p>All SDP media descriptions for streams represented by <code><a href="#mediastream">MediaStream</a></code> objects must include a label attribute
  (&quot;<code title="">a=label:</code>&quot;) whose value is the value of the <code><a href="#mediastream">MediaStream</a></code> object's <code title="dom-MediaStream-label"><a href="#dom-mediastream-label">label</a></code> attribute.
  [<cite><a class="bibref" rel="biblioentry" href="#bib-SDP">SDP</a></cite>] [<cite><a class="bibref" rel="biblioentry" href="#bib-SDPLABEL">SDPLABEL</a></cite>]</p>

  <p><a href="#peerconnection"><code>PeerConnection</code>s</a> must not generate any
  candidates for media streams whose media descriptions do not have a label attribute
  (&quot;<code title="">a=label:</code>&quot;). [<cite><a class="bibref" rel="biblioentry" href="#bib-ICE">ICE</a></cite>] [<cite><a class="bibref" rel="biblioentry" href="#bib-SDP">SDP</a></cite>] [<cite><a class="bibref" rel="biblioentry" href="#bib-SDPLABEL">SDPLABEL</a></cite>]</p>

  <p>When a user agent starts receiving media for a component and a candidate was
  provided for that component by a <a href="#peerconnection"><code>PeerConnection</code></a>, the user agent must follow these
  steps:</p>

  <ol>
    <li>
      <p>Let <var title="">connection</var> be the <code><a href="#peerconnection">PeerConnection</a></code> expecting this media.</p>
    </li>

    <li>
      <p>If there is already a <code><a href="#mediastream">MediaStream</a></code> object
      for the media stream to which this component belongs, then associate the component
      with that media stream and abort these steps. (Some media streams have multiple
      components; this API does not expose the role of these individual components in
      ICE.)</p>
    </li>

    <li>
      <p>Create a <code><a href="#mediastream">MediaStream</a></code> object to represent
      the media stream. Set its <code title="dom-MediaStream-label"><a href="#dom-mediastream-label">label</a></code> attribute to the value of the SDP Label
      attribute for that component's media stream.</p>
    </li>

    <li>
      <p>Queue a task to run the following substeps:</p>

      <ol>
        <li>
          <p>If the <var title="">connection</var>'s <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness
          state</a> is <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-CLOSED">CLOSED</a></code> (3), abort these steps.</p>
        </li>
<!--  close() was probably called just before this
     task ran  -->


        <li>
          <p>Add the newly created <code><a href="#mediastream">MediaStream</a></code>
          object to the end of <var title="">connection</var>'s <code title="dom-PeerConnection-remoteStreams"><a href="#widl-PeerConnection-remoteStreams">remoteStreams</a></code> array.</p>
        </li>

        <li>
          <p><a href="#fire-a-stream-event">Fire a stream event</a> named <code title="event-MediaStream-addstream"><a href="#event-mediastream-addstream">addstream</a></code> with the newly created
          <code><a href="#mediastream">MediaStream</a></code> object at the <var title="">connection</var> object.</p>
        </li>
      </ol>
    </li>
  </ol>

  <p>When a <a href="#peerconnection"><code>PeerConnection</code></a> finds that a stream
  from the remote peer has been removed (its port has been set to zero in a media
  description sent on the signaling channel), the user agent must follow these steps:</p>

  <ol>
    <li>
      <p>Let <var title="">connection</var> be the <code><a href="#peerconnection">PeerConnection</a></code> associated with the stream being
      removed.</p>
    </li>

    <li>
      <p>Let <var title="">stream</var> be the <code><a href="#mediastream">MediaStream</a></code> object that represents the media stream being
      removed, if any. If there isn't one, then abort these steps.</p>
    </li>

    <li>
      <p>By definition, <var title="">stream</var> is now <a href="#concept-stream-finished" title="concept-stream-finished">finished</a>.</p>

      <p class="note">A <span title="concept-task">task</span> is thus <span title="queue a task">queued</span> to update <var title="">stream</var> and fire an
      event.</p>
    </li>

    <li>
      <p>Queue a task to run the following substeps:</p>

      <ol>
        <li>
          <p>If the <var title="">connection</var>'s <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness
          state</a> is <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-NEW">CLOSED</a></code> (3), abort these steps.</p>
        </li>
<!--  close() was probably called just before this
     task ran  -->


        <li>
          <p>Remove <var title="">stream</var> from <var title="">connection</var>'s
          <code title="dom-PeerConnection-remoteStreams"><a href="#widl-PeerConnection-remoteStreams">remoteStreams</a></code> array.</p>
        </li>

        <li>
          <p><a href="#fire-a-stream-event">Fire a stream event</a> named <code title="event-MediaStream-removestream"><a href="#event-mediastream-removestream">removestream</a></code> with <var title="">stream</var> at the <var title="">connection</var> object.</p>
        </li>
      </ol>
    </li>
  </ol>

  <p>The task source for the <span title="concept-task">tasks</span> listed
  in this section is the networking task source.</p>

  <p class="warning">To prevent network sniffing from allowing a fourth party to
  establish a connection to a peer using the information sent out-of-band to the other
  peer and thus spoofing the client, the configuration information should always be
  transmitted using an encrypted connection.</p>

  <div id="peerconnection" class="section">
  <h3><span class="secno">4.1 </span>PeerConnection</h3>

  <pre class="idl"><span class="idlInterface" id="idl-def-PeerConnection">[<span class="extAttr">Constructor (in DOMString configuration, in SignalingCallback signalingCallback)</span>]
interface <span class="idlInterfaceID">PeerConnection</span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-PeerConnection-processSignalingMessage-void-DOMString-message">processSignalingMessage</a></span> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">message</span></span>);</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-NEW">NEW</a></span> = <span class="idlConstValue">0</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-NEGOTIATING">NEGOTIATING</a></span> = <span class="idlConstValue">1</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-ACTIVE">ACTIVE</a></span> = <span class="idlConstValue">2</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-CLOSING">CLOSING</a></span> = <span class="idlConstValue">4</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-CLOSED">CLOSED</a></span> = <span class="idlConstValue">3</span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>unsigned short</a></span> <span class="idlAttrName"><a href="#widl-PeerConnection-readyState">readyState</a></span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-ICE_GATHERING">ICE_GATHERING</a></span> = <span class="idlConstValue">0x100</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-ICE_WAITING">ICE_WAITING</a></span> = <span class="idlConstValue">0x200</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-ICE_CHECKING">ICE_CHECKING</a></span> = <span class="idlConstValue">0x300</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-ICE_CONNECTED">ICE_CONNECTED</a></span> = <span class="idlConstValue">0x400</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-ICE_COMPLETED">ICE_COMPLETED</a></span> = <span class="idlConstValue">0x500</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-ICE_FAILED">ICE_FAILED</a></span> = <span class="idlConstValue">0x600</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-ICE_CLOSED">ICE_CLOSED</a></span> = <span class="idlConstValue">00x700</span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>unsigned short</a></span> <span class="idlAttrName"><a href="#widl-PeerConnection-iceState">iceState</a></span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-SDP_IDLE">SDP_IDLE</a></span> = <span class="idlConstValue">0x1000</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-SDP_WAITING">SDP_WAITING</a></span> = <span class="idlConstValue">0x2000</span>;</span>
<span class="idlConst">    const <span class="idlConstType"><a>unsigned short</a></span> <span class="idlConstName"><a href="#widl-PeerConnection-SDP_GLARE">SDP_GLARE</a></span> = <span class="idlConstValue">0x3000</span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>unsigned short</a></span> <span class="idlAttrName"><a href="#widl-PeerConnection-sdpState">sdpState</a></span>;</span>
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-PeerConnection-addStream-void-MediaStream-stream-MediaStreamHints-hints">addStream</a></span> (<span class="idlParam"><span class="idlParamType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></span> <span class="idlParamName">stream</span></span>, <span class="idlParam"><span class="idlParamType"><a>MediaStreamHints</a></span> <span class="idlParamName">hints</span></span>);</span>
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-PeerConnection-removeStream-void-MediaStream-stream">removeStream</a></span> (<span class="idlParam"><span class="idlParamType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></span> <span class="idlParamName">stream</span></span>);</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a>[]</span>  <span class="idlAttrName"><a href="#widl-PeerConnection-localStreams">localStreams</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a>[]</span>  <span class="idlAttrName"><a href="#widl-PeerConnection-remoteStreams">remoteStreams</a></span>;</span>
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-PeerConnection-close-void">close</a></span> ();</span>
<span class="idlAttribute">             attribute <span class="idlAttrType"><a>Function</a>?</span>      <span class="idlAttrName"><a href="#widl-PeerConnection-onconnecting">onconnecting</a></span>;</span>
<span class="idlAttribute">             attribute <span class="idlAttrType"><a>Function</a>?</span>      <span class="idlAttrName"><a href="#widl-PeerConnection-onopen">onopen</a></span>;</span>
<span class="idlAttribute">             attribute <span class="idlAttrType"><a>Function</a>?</span>      <span class="idlAttrName"><a href="#widl-PeerConnection-onstatechange">onstatechange</a></span>;</span>
<span class="idlAttribute">             attribute <span class="idlAttrType"><a>Function</a>?</span>      <span class="idlAttrName"><a href="#widl-PeerConnection-onaddstream">onaddstream</a></span>;</span>
<span class="idlAttribute">             attribute <span class="idlAttrType"><a>Function</a>?</span>      <span class="idlAttrName"><a href="#widl-PeerConnection-onremovestream">onremovestream</a></span>;</span>
};</span>
</pre><div id="attributes-4" class="section"><h4><span class="secno">4.1.1 </span>Attributes</h4><dl class="attributes"><dt id="widl-PeerConnection-iceState"><code>iceState</code> of type <span class="idlAttrType"><a>unsigned short</a></span>, readonly</dt><dd>
      <p>The <dfn id="dom-peerconnection-icestate" title="dom-PeerConnection-iceState"><code title="">iceState</code></dfn> attribute
      must return the state of the <code><a href="#peerconnection">PeerConnection</a></code> ICE Agent 
      <a href="#dom-peerconnection-icestate"><code>PeerConnection</code> ICE
      state</a>, represented by a number from the following list:</p>

      <dl>
        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-NEW"><a href="#widl-PeerConnection-NEW">NEW</a></code>
        (0)</dt>

        <dd>The object was just created, and no networking has yet occurred.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-GATHERING"><a href="#widl-PeerConnection-ICE_GATHERING">ICE_GATHERING</a></code> (0x100)</dt>

        <dd>The ICE Agent is attempting to establish a gather addresses.</dd>

         <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-ICE_WAITING"><a href="#widl-PeerConnection-ICE_WAITING">ICE_WAITING</a></code> (0x200)</dt>

        <dd>The ICE Agent is waiting for candidates from the other side before it
        can start checking.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-CHECKING"><a href="#widl-PeerConnection-ICE_CHECKING">ICE_CHECKING</a></code> (0x300)</dt>
       <dd>The ICE Agent is checking candidates but has not yet found a connection.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-CONNECTED"><a href="#widl-PeerConnection-ICE_CONNECTED">ICE_CONNECTED</a></code> (0x400)</dt>
         <dd>The ICE Agent has found a connection but is still checking other
        candidates to see if there is a better connection.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-COMPLETED"><a href="#widl-PeerConnection-ICE_COMPLETED">ICE_COMPLETED</a></code> (0x500)</dt>
        <dd>The ICE Agent has finished checking and found a connection.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-ICE_FAILED"><a href="#widl-PeerConnection-ICE_FAILED">ICE_FAILED</a></code> (0x600)</dt>
        <dd>The ICE Agent is finished checking all candidates and failed to find a connection.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-ICE_CLOSED">ICE_CLOSED</a></code> (0x700)</dt>
        <dd>The ICE Agent has shut down and is no longer responding to STUN requests.</dd>
     </dl>
    <div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-localStreams"><code>localStreams</code> of type array of <span class="idlAttrType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></span>, readonly</dt><dd>
      <p>Returns a live array containing the streams that the user agent is currently
      attempting to transmit to the remote peer (those that were added with <code title="dom-PeerConnection-addStream"><a href="#widl-PeerConnection-addStream-void-MediaStream-stream-MediaStreamHints-hints">addStream()</a></code>).</p>

      <p>Specifically, it must return the read-only <code><a href="#mediastream">MediaStream</a></code> array that the attribute was set to when the
      <code><a href="#peerconnection">PeerConnection</a></code>'s constructor ran.</p>
    <div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-onaddstream"><code>onaddstream</code> of type <span class="idlAttrType"><a>Function</a></span>, nullable</dt><dd>This event handler, of <span title="event handler event type">event handler event
    type</span> <code title="event-MediaStream-addstream"><a href="#event-mediastream-addstream">addstream</a></code>, must be supported by all objects
    implementing the <code><a href="#peerconnection">PeerConnection</a></code>
    interface.<div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-onconnecting"><code>onconnecting</code> of type <span class="idlAttrType"><a>Function</a></span>, nullable</dt><dd>This event handler, of <span title="event handler event type">event handler event
    type</span> <code title="event-MediaStream-connecting"><a href="#event-mediastream-connecting">connecting</a></code>, must be supported by all
    objects implementing the <code><a href="#peerconnection">PeerConnection</a></code>
    interface.<div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-onopen"><code>onopen</code> of type <span class="idlAttrType"><a>Function</a></span>, nullable</dt><dd>This event handler, of <span title="event handler event type">event handler event
    type</span> <code title="event-MediaStream-open"><a href="#event-mediastream-open">open</a></code>, must be supported by all objects
    implementing the <code><a href="#peerconnection">PeerConnection</a></code>
    interface.<div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-onremovestream"><code>onremovestream</code> of type <span class="idlAttrType"><a>Function</a></span>, nullable</dt><dd>This event handler, of <span title="event handler event type">event handler event
    type</span> <code title="event-MediaStream-removestream"><a href="#event-mediastream-removestream">removestream</a></code>, must be supported by all
    objects implementing the <code><a href="#peerconnection">PeerConnection</a></code>
    interface.<div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-onstatechange"><code>onstatechange</code> of type <span class="idlAttrType"><a>Function</a></span>, nullable</dt><dd>This event handler, of <span title="event handler event type">event handler event
    type</span> <code title="event-MediaStream-open"><a href="#event-mediastream-open">open</a></code>, must be supported by all objects
    implementing the <code><a href="#peerconnection">PeerConnection</a></code>
    interface. It is called any time the readyState, iceState, or sdpState
    changes. <div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-readyState"><code>readyState</code> of type <span class="idlAttrType"><a>unsigned short</a></span>, readonly</dt><dd>
      <p>The <dfn id="dom-peerconnection-readystate" title="dom-PeerConnection-readyState"><code title="">readyState</code></dfn> attribute
      must return the <code><a href="#peerconnection">PeerConnection</a></code> object's
      <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness
      state</a>, represented by a number from the following list:</p>

      <dl>
        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-NEW"><a href="#widl-PeerConnection-NEW">NEW</a></code>
        (0)</dt>

        <dd>The object was just created, and no networking has yet occurred.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-NEGOTIATING"><a href="#widl-PeerConnection-NEGOTIATING">NEGOTIATING</a></code> (1)</dt>

        <dd>The user agent is attempting to establish an connection with the ICE
        Agent and to negotiate codecs with the SDP Agent.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-ACTIVE"><a href="#widl-PeerConnection-ACTIVE">ACTIVE</a></code> (2)</dt>

        <dd>The ICE Agent has found a connection the SDP Agent has performed a
        round of codec negotiation. It is possible for whatever media was
        negotiated to flow.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-CLOSING"><a href="#widl-PeerConnection-CLOSING">CLOSING</a></code> (4)</dt>

         <dd> The <code><a href="#peerconnection">PeerConnection</a></code>
         object is terminating all media and is in the process of closing the
         Ice Agent and SDP Agent. </dd>
        
        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-CLOSED">CLOSED</a></code> (3)</dt>

       <dd>The connection is closed. </dd>
      </dl>
    <div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-remoteStreams"><code>remoteStreams</code> of type array of <span class="idlAttrType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></span>, readonly</dt><dd>
      <p>Returns a live array containing the streams that the user agent is currently
      receiving from the remote peer.</p>

      <p>Specifically, it must return the read-only <code><a href="#mediastream">MediaStream</a></code> array that the attribute was set to when the
      <code><a href="#peerconnection">PeerConnection</a></code>'s constructor ran.</p>

      <p>This array is updated when <code title="event-MediaStream-addstream"><a href="#event-mediastream-addstream">addstream</a></code> and <code title="event-MediaStream-removestream"><a href="#event-mediastream-removestream">removestream</a></code> events are fired.</p>
    <div><em>No exceptions.</em></div></dd><dt id="widl-PeerConnection-sdpState"><code>sdpState</code> of type <span class="idlAttrType"><a>unsigned short</a></span>, readonly</dt><dd> <p>The <dfn id="dom-peerconnection-sdpstate" title="dom-PeerConnection-sdpState"><code title="">sdpState</code></dfn> attribute
   must return the state of the <code><a href="#peerconnection">PeerConnection</a></code> SDP Agent , represented by
   a number from the following list:</p>

      <dl>
        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-NEW"><a href="#widl-PeerConnection-NEW">NEW</a></code>
        (0)</dt>

        <dd>The object was just created, and no networking has yet occurred.</dd>

       <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-SDP_IDLE"><a href="#widl-PeerConnection-SDP_IDLE">SDP_IDLE</a></code> (0x1000)</dt>

        <dd>At least one SDP offer or answer has been exchange and the SDP Agent
        is ready to send an SDP offer or receive an SDP answer.</dd>

         <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-SDP_WAITING"><a href="#widl-PeerConnection-SDP_WAITING">SDP_WAITING</a></code> (0x2000)</dt>

        <dd>The SDP Agent has sent and offer and is waiting for a answer.</dd>

        <dt><code><a href="#peerconnection">PeerConnection</a></code> . <code title="dom-PeerConnection-SDP_GLARE"><a href="#widl-PeerConnection-SDP_GLARE">SDP_GLARE</a></code> (0x3000)</dt>

        <dd>The SDP Agent received an offer while waiting for an answer and now
        much wait a rondom amount of time before retrying to send the offer.</dd>

      </dl>
    <div><em>No exceptions.</em></div></dd></dl></div><div id="methods-8" class="section"><h4><span class="secno">4.1.2 </span>Methods</h4><dl class="methods"><dt id="widl-PeerConnection-addStream-void-MediaStream-stream-MediaStreamHints-hints"><code>addStream</code></dt><dd>
      <p>Attempts to starting sending the given stream to the remote peer.
      The format for the MediaStreamHints objects is currently undefined
      by the specification.</p>

      <p>When the other peer starts sending a stream in this manner, an <code title="event-MediaStream-addstream"><a href="#event-mediastream-addstream">addstream</a></code> event is fired at the
      <code><a href="#peerconnection">PeerConnection</a></code> object.</p>
<!--  </ol>  -->


      <p>When the <dfn id="dom-peerconnection-addstream" title="dom-PeerConnection-addStream"><code title="">addStream()</code></dfn> method is
      invoked, the user agent must run the following steps:</p>

      <ol>
        <li>
          <p>Let <var title="">stream</var> be the method's first argument.</p>
        </li>

        <li>
          <p>Let <var title="">hints</var> be the method's second argument.</p>
        </li>

        <li>
          <p>If the <code><a href="#peerconnection">PeerConnection</a></code> object's
          <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness
          state</a> is <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-NEW">CLOSED</a></code> (3), throw an
          <code>INVALID_STATE_ERR</code> exception.</p>
        </li>

        <li>
          <p>If <var title="">stream</var> is already in the <code><a href="#peerconnection">PeerConnection</a></code> object's <code title="dom-PeerConnection-localStreams"><a href="#widl-PeerConnection-localStreams">localStreams</a></code> object, then abort
          these steps.</p>
        </li>

        <li>
          <p>Add <var title="">stream</var> to the end of the <code><a href="#peerconnection">PeerConnection</a></code> object's <code title="dom-PeerConnection-localStreams"><a href="#widl-PeerConnection-localStreams">localStreams</a></code> object.</p>
        </li>

        <li>
          <p>Return from the method.</p>
        </li>

        <li>
          <p>Parse the <var title="">hints</var> provided by the application
          and apply them to the MediaStream, if possible.
          </p>
        </li>
        <li>
          <p>Have the <code><a href="#peerconnection">PeerConnection</a></code> add a
          media stream for <var title="">stream</var> the next time the user agent
          <span title="provide a stable state">provides a stable state</span>. Any other
          pending stream additions and removals must be processed at the same time.</p>
        </li>
      </ol>
    <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">stream</td><td class="prmType"><code><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">hints</td><td class="prmType"><code><a>MediaStreamHints</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd><dt id="widl-PeerConnection-close-void"><code>close</code></dt><dd>
      <p>When the <dfn id="dom-peerconnection-close" title="dom-PeerConnection-close"><code title="">close()</code></dfn> method is invoked,
      the user agent must run the following steps:</p>

      <ol>
        <li>
          <p>If the <code><a href="#peerconnection">PeerConnection</a></code> object's
          <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness
          state</a> is <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-CLOSED">CLOSED</a></code> (3), throw an
          <code>INVALID_STATE_ERR</code> exception.</p>
        </li>

        <li>
          <p>Destroy the <a href="#peerconnection-ice-agent"><code>PeerConnection</code>
          ICE Agent</a>, abruptly ending any active ICE processing and any active
          streaming, and releasing any relevant resources (e.g. TURN permissions).</p>
        </li>

        <li>
          <p>Set the object's <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness
          state</a> to <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-CLOSED">CLOSED</a></code> (3).</p>
        </li>
<!-- 
   <li><p>Queue a task to fire a simple
   event named <code title="event-MediaStream-close">close</code> at the
   <code>PeerConnection</code> object.</p></p></li>
 -->

      </ol>

      <p class="note">The <code title="dom-PeerConnection-localStreams"><a href="#widl-PeerConnection-localStreams">localStreams</a></code> and <code title="dom-PeerConnection-remoteStreams"><a href="#widl-PeerConnection-remoteStreams">remoteStreams</a></code> objects remain in the
      state they were in when the object was closed.</p>
    <div><em>No parameters.</em></div><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd><dt id="widl-PeerConnection-processSignalingMessage-void-DOMString-message"><code>processSignalingMessage</code></dt><dd>
      <p>When a message is relayed from the remote peer over the signaling channel is
      received by the Web application, pass it to the user agent by calling the
      <code title="dom-PeerConnection-processSignalingMessage"><a href="#dom-peerconnection-processsignalingmessage">processSignalingMessage()</a></code>
      method.</p>

      <p>The order of messages is important. Passing messages to the user agent in a
      different order than they were generated by the remote peer's user agent can
      prevent a successful connection from being established or degrade the connection's
      quality if one is established.</p>

      <p>When the <dfn id="dom-peerconnection-processsignalingmessage" title="dom-PeerConnection-processSignalingMessage"><code title="&quot;&quot;">processSignalingMessage()</code></dfn> method is invoked, the user agent must
      run the following steps:</p>

      <ol>
        <li>
          <p>Let <var title="">message</var> be the method's argument.</p>
        </li>

        <li>
          <p>Let <var title="">connection</var> be the <code><a href="#peerconnection">PeerConnection</a></code> object on which the method was
          invoked.</p>
        </li>

        <li>
          <p>If <var title="">connection</var>'s <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness
          state</a> is <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-NEW">CLOSED</a></code> (3), throw an
          <code>INVALID_STATE_ERR</code> exception.</p>
        </li>

        <li>
          <p>If the first four characters of <var title="">message</var> are not
          &quot;<code title="">SDP</code>&quot; followed by a U+000A LINE FEED (LF) character, then
          abort these steps. (This indicates an error in the signaling channel
          implementation. User agents may report such errors to their developer consoles
          to aid debugging.)</p>

          <p class="note">Future extensions to the <code><a href="#peerconnection">PeerConnection</a></code> interface might use other prefix
          values to implement additional features.</p>
        </li>

        <li>
          <p>Let <var title="">sdp</var> be the string consisting of all but the first
          four characters of <var title="">message</var>.</p>
        </li>

        <li>
          <p> Pass the <var title="">sdp</var> to the <a href="#peerconnection-ice-agent"><code>PeerConnection</code> SDP Agent</a>  as a
          subsequent offer or answer, to be interpreted as appropriate given the current
          state of the SDP Agent. [<cite><a class="bibref" rel="biblioentry" href="#bib-ICE">ICE</a></cite>]</p>
        </li>
        
      </ol>

      <p>When a <a href="#peerconnection-ice-agent"><code>PeerConnection</code> ICE
      Agent</a> forms a connection to the the far side and enters the state
      ICECONNECTED, the user
      agent must queue a task that sets the <code><a href="#peerconnection">PeerConnection</a></code> object's <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness state</a>
      to <code title="dom-PeerConnection-ACTIVE"><a href="#widl-PeerConnection-ACTIVE">ACTIVE</a></code> (2) and then <span title="fire a simple event">fires a simple event</span> named <code title="event-MediaStream-open"><a href="#event-mediastream-open">open</a></code> at the
      <code><a href="#peerconnection">PeerConnection</a></code> object.</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">message</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>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd><dt id="widl-PeerConnection-removeStream-void-MediaStream-stream"><code>removeStream</code></dt><dd>
      <p>Stops sending the given stream to the remote peer.</p>

      <p>When the other peer stops sending a stream in this manner, a <code title="event-MediaStream-removestream"><a href="#event-mediastream-removestream">removestream</a></code> event is fired at the
      <code><a href="#peerconnection">PeerConnection</a></code> object.</p>

      <p>When the <dfn id="dom-peerconnection-removestream" title="dom-PeerConnection-removeStream"><code title="">removeStream()</code></dfn> method
      is invoked, the user agent must run the following steps:</p>

      <ol>
        <li>
          <p>Let <var title="">stream</var> be the method's argument.</p>
        </li>

        <li>
          <p>If the <code><a href="#peerconnection">PeerConnection</a></code> object's
          <a href="#peerconnection-readiness-state"><code>PeerConnection</code> readiness
          state</a> is <code title="dom-PeerConnection-CLOSED"><a href="#widl-PeerConnection-CLOSED">CLOSED</a></code> (3), throw an
          <code>INVALID_STATE_ERR</code> exception.</p>
        </li>

        <li>
          <p>If <var title="">stream</var> is not in the <code><a href="#peerconnection">PeerConnection</a></code> object's <code title="dom-PeerConnection-localStreams"><a href="#widl-PeerConnection-localStreams">localStreams</a></code> object, then abort
          these steps.</p>
        </li>

        <li>
          <p>Remove <var title="">stream</var> from the <code><a href="#peerconnection">PeerConnection</a></code> object's <code title="dom-PeerConnection-localStreams"><a href="#widl-PeerConnection-localStreams">localStreams</a></code> object.</p>
        </li>

        <li>
          <p>Return from the method.</p>
        </li>

        <li>
          <p>Have the <code><a href="#peerconnection">PeerConnection</a></code>remove the
          media stream for <var title="">stream</var> the next time the user agent
          <span title="provide a stable state">provides a stable state</span>. Any other
          pending stream additions and removals must be processed at the same time.</p>
        </li>
<!--  section 9.1.1.2  -->

      </ol>
    <table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">stream</td><td class="prmType"><code><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div><div id="constants-2" class="section"><h4><span class="secno">4.1.3 </span>Constants</h4><dl class="constants"><dt id="widl-PeerConnection-ACTIVE"><code>ACTIVE</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd> A connection has been formed and if any media streams were
    successfully negotiated, any relevant media can be streaming.</dd><dt id="widl-PeerConnection-CLOSED"><code>CLOSED</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The <code title="dom-PeerConnection-close"><a href="#dom-peerconnection-close">close()</a></code> method has been invoked.</dd><dt id="widl-PeerConnection-CLOSING"><code>CLOSING</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The object is starting to shut down after the  <code title="dom-PeerConnection-close"><a href="#dom-peerconnection-close">close()</a></code> method has been invoked.</dd><dt id="widl-PeerConnection-ICE_CHECKING"><code>ICE_CHECKING</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The ICE Agent is checking candidates but has not yet found a connection
   that works.</dd><dt id="widl-PeerConnection-ICE_CLOSED"><code>ICE_CLOSED</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The ICE Agent is terminating and will no longer repined to STUN
 connectivity checks.</dd><dt id="widl-PeerConnection-ICE_COMPLETED"><code>ICE_COMPLETED</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The ICE Agent has finished checking all candidates and a connection has
     been formed.</dd><dt id="widl-PeerConnection-ICE_CONNECTED"><code>ICE_CONNECTED</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The ICE Agent has found at least one candidate that works but is still checking.</dd><dt id="widl-PeerConnection-ICE_FAILED"><code>ICE_FAILED</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The ICE Agent has finished checking all candidates and no connection
     was worked.</dd><dt id="widl-PeerConnection-ICE_GATHERING"><code>ICE_GATHERING</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The ICE Agent is gather addresses that can be used.</dd><dt id="widl-PeerConnection-ICE_WAITING"><code>ICE_WAITING</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>THE ICE Agent has complete gathering addresses and is waiting for candidates
      to start checking. </dd><dt id="widl-PeerConnection-NEGOTIATING"><code>NEGOTIATING</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The peerConenction object is attempting to get to the point wehre media
    can flow.</dd><dt id="widl-PeerConnection-NEW"><code>NEW</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>The object was just created and its ICE and SDP Agent have not yet been started.</dd><dt id="widl-PeerConnection-SDP_GLARE"><code>SDP_GLARE</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>Both side sent SDP offers at the same time and the SDP Agent is waiting to
        be able to retransmit the SDP offer.</dd><dt id="widl-PeerConnection-SDP_IDLE"><code>SDP_IDLE</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd>A valid offer anser pair has been exchanged and the SDP Agent is waiting
      for the next SDP transaction.</dd><dt id="widl-PeerConnection-SDP_WAITING"><code>SDP_WAITING</code> of type <span class="idlConstType"><a>unsigned short</a></span></dt><dd> The SDP Agent has sent an SDP offer and is waiting for a response.</dd></dl></div>

  <pre class="idl"><span class="idlImplements"><a href="#idl-def-PeerConnection" class="idlType"><code>PeerConnection</code></a> implements <a>EventTarget</a>;</span></pre><div class="idlImplementsDesc"><p>All instances of the <code><a href="#idl-def-PeerConnection" class="idlType"><code>PeerConnection</code></a></code> type are defined to also implement the <a>EventTarget</a> interface.</p></div>
  </div>

  <div id="signalingcallback" class="section">
  <h3><span class="secno">4.2 </span>SignalingCallback</h3>

  <pre class="idl"><span class="idlInterface" id="idl-def-SignalingCallback">[<span class="extAttr">Callback=FunctionOnly, NoInterfaceObject</span>]
interface <span class="idlInterfaceID">SignalingCallback</span> {
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-SignalingCallback-handleEvent-void-DOMString-message-PeerConnection-source">handleEvent</a></span> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">message</span></span>, <span class="idlParam"><span class="idlParamType"><a href="#idl-def-PeerConnection" class="idlType"><code>PeerConnection</code></a></span> <span class="idlParamName">source</span></span>);</span>
};</span>
</pre><div id="methods-9" class="section"><h4><span class="secno">4.2.1 </span>Methods</h4><dl class="methods"><dt id="widl-SignalingCallback-handleEvent-void-DOMString-message-PeerConnection-source"><code>handleEvent</code></dt><dd>Def TBD<table class="parameters"><tr><th>Parameter</th><th>Type</th><th>Nullable</th><th>Optional</th><th>Description</th></tr><tr><td class="prmName">message</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">source</td><td class="prmType"><code><a href="#idl-def-PeerConnection" class="idlType"><code>PeerConnection</code></a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>
  </div>

  <div id="examples-2" class="section">
  <h3><span class="secno">4.3 </span>Examples</h3>

  <div class="example">
    <p>When two peers decide they are going to set up a connection to each other, they
    both go through these steps. The STUN/TURN server configuration describes a server
    they can use to get things like their public IP address or to set up NAT traversal.
    They also have to send data for the signaling channel to each other using the same
    out-of-band mechanism they used to establish that they were going to communicate in
    the first place.</p>
    <pre>// the first argument describes the STUN/TURN server configuration
var local = new PeerConnection('TURNS example.net', sendSignalingChannel);
local.signalingChannel(...); // if we have a message from the other side, pass it along here

// (aLocalStream is some LocalMediaStream object)
local.addStream(aLocalStream); // start sending video

function sendSignalingChannel(message) {
  ... // send message to the other side via the signaling channel
}

function receiveSignalingChannel (message) {
  // call this whenever we get a message on the signaling channel
  local.signalingChannel(message);
}

local.onaddstream = function (event) {
  // (videoElement is some &lt;video&gt; element)
  videoElement.src = URL.getObjectURL(event.stream);
};
</pre>
  </div>
  </div>
  </div>

  <div id="the-data-stream" class="section">
  
<!-- OddPage -->
<h2><span class="secno">5. </span>The data stream</h2>

  <p class="note">Although progress is being made, there is currently not enough
  agreement on the data channel to write it up. This section will be filled in as rough
  consensus is reached.</p>
  </div>

  <div id="garbage-collection" class="section">
  
<!-- OddPage -->
<h2><span class="secno">6. </span>Garbage collection</h2>

  <p>A <code>Window</code> object <dfn id="concept-peerconnection-owner" title="concept-PeerConnection-owner">has a strong reference</dfn> to any <code><a href="#peerconnection">PeerConnection</a></code> objects created from the constructor whose
  global object is that <code>Window</code> object.</p>
<!--  we
  could be less strict here, e.g. dropping the reference when there's
  no way for an event to be fired because there's no event handlers
  registered and there's no way for the remote peer to notice anything
  because no media is streaming; or e.g. dropping the reference when
  the object reaches the CLOSED state. But as dropping the reference
  in those cases is black-box indistinguishable from keeping the
  reference, I haven't bothered to work out the exact rules. If you do
  change this, see the /unloading document cleanup steps/.  -->

  </div>

  <div id="event-definitions" class="section">
  
<!-- OddPage -->
<h2><span class="secno">7. </span>Event definitions</h2>

  <p>The <code title="event-MediaStream-addstream"><a href="#event-mediastream-addstream">addstream</a></code> and <code title="event-MediaStream-removestream"><a href="#event-mediastream-removestream">removestream</a></code> events use the <code><a href="#mediastreamevent">MediaStreamEvent</a></code> interface:</p>

  <div id="mediastreamevent" class="section">
  <h3><span class="secno">7.1 </span>MediaStreamEvent</h3>

  <p><dfn id="fire-a-stream-event" title="fire a stream event">Firing a stream event
  named <var title="">e</var></dfn> with a <code><a href="#mediastream">MediaStream</a></code> <var title="">stream</var> means that an event
  with the name <var title="">e</var>, which does not bubble (except where otherwise
  stated) and is not cancelable (except where otherwise stated), and which uses the
  <code><a href="#mediastreamevent">MediaStreamEvent</a></code> interface with the
  <code title="dom-MediaStreamEvent-stream"><a href="#dom-mediastreamevent-stream">stream</a></code> attribute set to <var title="">stream</var>, must be created and dispatched at the given target.</p>

  <pre class="idl"><span class="idlInterface" id="idl-def-MediaStreamEvent">interface <span class="idlInterfaceID">MediaStreamEvent</span> : <span class="idlSuperclass"><a>Event</a></span> {
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a>?</span> <span class="idlAttrName"><a href="#widl-MediaStreamEvent-stream">stream</a></span>;</span>
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-MediaStreamEvent-initMediaStreamEvent-void-DOMString-typeArg-boolean-canBubbleArg-boolean-cancelableArg-MediaStream-streamArg">initMediaStreamEvent</a></span> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">typeArg</span></span>, <span class="idlParam"><span class="idlParamType"><a>boolean</a></span> <span class="idlParamName">canBubbleArg</span></span>, <span class="idlParam"><span class="idlParamType"><a>boolean</a></span> <span class="idlParamName">cancelableArg</span></span>, <span class="idlParam"><span class="idlParamType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a>?</span> <span class="idlParamName">streamArg</span></span>);</span>
};</span>
</pre><div id="attributes-5" class="section"><h4><span class="secno">7.1.1 </span>Attributes</h4><dl class="attributes"><dt id="widl-MediaStreamEvent-stream"><code>stream</code> of type <span class="idlAttrType"><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></span>, readonly, nullable</dt><dd>
      <p>The <dfn id="dom-mediastreamevent-stream" title="dom-MediaStreamEvent-stream"><code>stream</code></dfn> attribute represents the
      <code><a href="#mediastream">MediaStream</a></code> object associated with the
      event.</p>
    <div><em>No exceptions.</em></div></dd></dl></div><div id="methods-10" class="section"><h4><span class="secno">7.1.2 </span>Methods</h4><dl class="methods"><dt id="widl-MediaStreamEvent-initMediaStreamEvent-void-DOMString-typeArg-boolean-canBubbleArg-boolean-cancelableArg-MediaStream-streamArg"><code>initMediaStreamEvent</code></dt><dd>
      <p>The <dfn id="dom-mediastreamevent-initmediastreamevent" title="dom-MediaStreamEvent-initMediaStreamEvent"><code>initMediaStreamEvent()</code></dfn>
      method must initialize the event in a manner analogous to the similarly-named
      method in the DOM Events interfaces. [<cite><a class="bibref" rel="biblioentry" href="#bib-DOM-LEVEL-3-EVENTS">DOM-LEVEL-3-EVENTS</a></cite>]</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">typeArg</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">canBubbleArg</td><td class="prmType"><code><a>boolean</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">cancelableArg</td><td class="prmType"><code><a>boolean</a></code></td><td class="prmNullFalse">✘</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr><tr><td class="prmName">streamArg</td><td class="prmType"><code><a href="#idl-def-MediaStream" class="idlType"><code>MediaStream</code></a></code></td><td class="prmNullTrue">✔</td><td class="prmOptFalse">✘</td><td class="prmDesc"></td></tr></table><div><em>No exceptions.</em></div><div><em>Return type: </em><code><a>void</a></code></div></dd></dl></div>
  </div>
  </div>

  <div class="informative section" id="event-summary">
  
<!-- OddPage -->
<h2><span class="secno">8. </span>Event summary</h2><p><em>This section is non-normative.</em></p>

  <p>The following event fires on <code><a href="#mediastream">MediaStream</a></code>
  objects:</p>

  <table>
    <tbody><tr>
      <th>Event name</th>

      <th>Interface</th>

      <th>Fired when...</th>
    </tr>

    </tbody><tbody>
      <tr>
        <td><dfn id="event-mediastream-ended" title="event-MediaStream-ended"><code>ended</code></dfn></td>

        <td><code>Event</code></td>

        <td>The <code><a href="#mediastream">MediaStream</a></code> object will no longer
        stream any data, either because the user revoked the permissions, or because the
        source device has been ejected, or because the remote peer stopped sending data,
        or because the <code title="dom-MediaStream-stop"><a href="#dom-mediastream-stop">stop()</a></code> method was invoked.</td>
      </tr>
    </tbody>
  </table>

  <p>The following events fire on <code><a href="#peerconnection">PeerConnection</a></code> objects:</p>

  <table>
    <tbody><tr>
      <th>Event name</th>

      <th>Interface</th>

      <th>Fired when...</th>
    </tr>

    </tbody><tbody>
      <tr>
        <td><dfn id="event-mediastream-connecting" title="event-MediaStream-connecting"><code>connecting</code></dfn></td>

        <td><code>Event</code></td>

        <td>The ICE Agent has begun negotiating with the peer. This can happen multiple
        times during the lifetime of the <code><a href="#peerconnection">PeerConnection</a></code> object.</td>
      </tr>

      <tr>
        <td><dfn id="event-mediastream-open" title="event-MediaStream-open"><code>open</code></dfn></td>

        <td><code>Event</code></td>

        <td>The ICE Agent has finished negotiating with the peer.</td>
      </tr>

      <tr>
        <td><dfn id="event-mediastream-message" title="event-MediaStream-message"><code>message</code></dfn></td>

        <td><code>MessageEvent</code></td>

        <td>A data UDP media stream message (to be defined) was
        received.</td>
      </tr>

      <tr>
        <td><dfn id="event-mediastream-addstream" title="event-MediaStream-addstream"><code>addstream</code></dfn></td>

        <td><code><a href="#mediastreamevent">MediaStreamEvent</a></code></td>

        <td>A new stream has been added to the <code title="dom-PeerConnection-remoteStreams"><a href="#widl-PeerConnection-remoteStreams">remoteStreams</a></code> array.</td>
      </tr>

      <tr>
        <td><dfn id="event-mediastream-removestream" title="event-MediaStream-removestream"><code>removestream</code></dfn></td>

        <td><code><a href="#mediastreamevent">MediaStreamEvent</a></code></td>

        <td>A stream has been removed from the <code title="dom-PeerConnection-remoteStreams"><a href="#widl-PeerConnection-remoteStreams">remoteStreams</a></code> array.</td>
      </tr>
    </tbody>
  </table>
  </div>

  <div id="application-html-peer-connection-data" class="section">
  
<!-- OddPage -->
<h2><span class="secno">9. </span>application/html-peer-connection-data</h2>

  <p>This registration is for community review and will be submitted to the IESG for
  review, approval, and registration with IANA.</p>
<!-- 
   To: ietf-types@iana.org
   Subject: Registration of media type application/html-peer-connection-data
   -->


  <dl>
    <dt>Type name:</dt>

    <dd>application</dd>

    <dt>Subtype name:</dt>

    <dd>html-peer-connection-data</dd>

    <dt>Required parameters:</dt>

    <dd>No required parameters</dd>

    <dt>Optional parameters:</dt>

    <dd>No optional parameters</dd>

    <dt>Encoding considerations:</dt>

    <dd>This MIME type defines a binary protocol format which uses UTF-8 for text
    encoding.</dd>

    <dt>Security considerations:</dt>

    <dd>
      <p>This format is used for encoding UDP packets transmitted by potentially hostile
      Web page content via a trusted user agent to a destination selected by a
      potentially hostile remote server. To prevent this mechanism from being abused for
      cross-protocol attacks, all the data in these packets is masked so as to appear to
      be random noise. The intent of this masking is to reduce the potential attack
      scenarios to those already possible previously.</p>

      <p>However, this feature still allows random data to be sent to destinations that
      might not normally have been able to receive them, such as to hosts within the
      victim's intranet. If a service within such an intranet cannot handle receiving UDP
      packets containing random noise, it might be vulnerable to attack from this
      feature.</p>
    </dd>

    <dt>Interoperability considerations:</dt>

    <dd>Rules for processing both conforming and non-conforming content are defined in
    this specification.</dd>

    <dt>Published specification:</dt>

    <dd>This document is the relevant specification.</dd>

    <dt>Applications that use this media type:</dt>

    <dd>This type is only intended for use with SDP. [<cite><a class="bibref" rel="biblioentry" href="#bib-SDP">SDP</a></cite>]</dd>

    <dt>Additional information:</dt>

    <dd>
      <dl>
        <dt>Magic number(s):</dt>

        <dd>No sequence of bytes can uniquely identify data in this format, as all data
        in this format is intentionally masked to avoid cross-protocol attacks.</dd>

        <dt>File extension(s):</dt>

        <dd>This format is not for use with files.</dd>

        <dt>Macintosh file type code(s):</dt>

        <dd>This format is not for use with files.</dd>
      </dl>
    </dd>

    <dt>Person &amp; email address to contact for further information:</dt>

    <dd>Daniel C. Burnett &lt;dburnett@voxeo.com&gt;</dd>

    <dt>Intended usage:</dt>

    <dd>Common</dd>

    <dt>Restrictions on usage:</dt>

    <dd>No restrictions apply.</dd>

    <dt>Author:</dt>

    <dd>Daniel C. Burnett &lt;dburnett@voxeo.com&gt;</dd>

    <dt>Change controller:</dt>

    <dd>W3C</dd>
  </dl>

  <p>Fragment identifiers cannot be used with <code><a href="#application-html-peer-connection-data">application/html-peer-connection-data</a></code>
  as URLs cannot be used to identify streams that use this format.</p>
  </div>
 
  <div class="appendix section" id="acknowledgements">
  
<!-- OddPage -->
<h2><span class="secno">A. </span>Acknowledgements</h2>

  <p>The editors wish to thank the Working Group chairs, Harald Alvestrand and Stefan
  Håkansson, for their support.</p>
  </div>


<div id="references" class="appendix section">
<!-- OddPage -->
<h2><span class="secno">B. </span>References</h2><div id="normative-references" class="section"><h3><span class="secno">B.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-DOM-LEVEL-3-EVENTS">[DOM-LEVEL-3-EVENTS]</dt><dd>Björn Höhrmann; Tom Pixley; Philippe Le Hégaret. <a href="http://www.w3.org/TR/2011/WD-DOM-Level-3-Events-20110531/"><cite>Document Object Model (DOM) Level 3 Events Specification.</cite></a> 31 May 2011. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2011/WD-DOM-Level-3-Events-20110531/">http://www.w3.org/TR/2011/WD-DOM-Level-3-Events-20110531/</a> 
</dd><dt id="bib-FILE-API">[FILE-API]</dt><dd>Arun Ranganathan. <a href="http://www.w3.org/TR/2009/WD-FileAPI-20091117/"><cite>File API.</cite></a> 17 November 2009. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2009/WD-FileAPI-20091117/">http://www.w3.org/TR/2009/WD-FileAPI-20091117/</a> 
</dd>

 <dt id="bib-ICE">[ICE]</dt><dd>J. Rosenberg <a href="http://tools.ietf.org/html/rfc5245"><cite>Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols.</cite></a> April 2010. Internet RFC 5245. URL: <a href="http://tools.ietf.org/html/rfc5245">http://tools.ietf.org/html/rfc5245</a></dd>

 <dt id="bib-SDP">[SDP]</dt><dd>J. Rosenberg, H. Schulzrinne. <a href="http://tools.ietf.org/html/rfc3264"><cite>An Offer/Answer Model with the Session Description Protocol (SDP).</cite></a> June 2002. Internet RFC 3264. URL: <a href="http://tools.ietf.org/html/rfc3264">http://tools.ietf.org/html/rfc3264</a></dd>

 <dt id="bib-SDPLABEL">[SDPLABEL]</dt><dd>O. Levin, G. Camarillo. <a href="http://tools.ietf.org/html/rfc4574"><cite>The Session Description Protocol (SDP) Label Attribute.</cite></a> August 2006. Internet RFC 4574. URL: <a href="http://tools.ietf.org/html/rfc4574">http://tools.ietf.org/html/rfc4574</a></dd>

 <dt id="bib-STUN">[STUN]</dt><dd>J. Rosenberg, R. Mahy, P. Matthews, D. Wing. <a href="http://tools.ietf.org/html/rfc5389"><cite>Session Traversal Utilities for NAT (STUN).</cite></a> October 2008. Internet RFC 5389. URL: <a href="http://tools.ietf.org/html/rfc5389">http://tools.ietf.org/html/rfc5389</a></dd>

 <dt id="bib-TURN">[TURN]</dt><dd>P. Mahy, P. Matthews, J. Rosenberg. <a href="http://tools.ietf.org/html/rfc5766"><cite>Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN).</cite></a> April 2010. Internet RFC 5766. URL: <a href="http://tools.ietf.org/html/rfc5766">http://tools.ietf.org/html/rfc5766</a></dd>

<dt id="bib-WEBIDL">[WEBIDL]</dt><dd>Cameron McCormack. <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219"><cite>Web IDL.</cite></a> 19 December 2008. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219">http://www.w3.org/TR/2008/WD-WebIDL-20081219</a> 
</dd>

</dl></div><div id="informative-references" class="section"><h3><span class="secno">B.2 </span>Informative references</h3><p>No informative references.</p></div></div></body></html>