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<!DOCTYPE html>
<html lang="en" dir="ltr">
<head>
<meta charset="utf-8">
<link href="webrtc.css" rel="stylesheet">
<title>WebRTC Extensions</title>
<script class="remove" src="https://www.w3.org/Tools/respec/respec-w3c"></script>
<script class="remove" src="webrtc-extensions.js" ></script>
</head>
<body>
<section id="abstract">
<p>
This document defines a set of ECMAScript APIs in WebIDL to extend the WebRTC 1.0 API.
</p>
</section>
<section id="sotd">
<p>The API is based on preliminary work done in the W3C WEBRTC Working Group.</p>
</section>
<section class="informative" id="intro">
<h2>Introduction</h2>
<p>
This document contains proposed extensions to the [[WEBRTC]] specification.
Some of these extensions were originally included within the [[WEBRTC]] specification,
but needed to be removed due to lack of implementation experience. Others were not
sufficiently mature to be incorporated into that specification when they were developed,
but were too small to warrant creation of a separate document.
</p>
<p>
This document contains some sections extending one specific interface or dictionary in
the base specification; in this case the extension is only described in an individual
section. Where an extension affects multiple interfaces or dictionaries, a subsection
in the "Overviews" section describes the extension as a whole, while normative text
is provided in sections relating to the individual interfaces.
</p>
<p>
As extensions mature and gain implementation experience, they may move from this document
to the base specification if WG consensus emerges to do so.
</p>
</section>
<section id="conformance">
<p>This specification defines conformance criteria that apply to a single
product: the <dfn>user agent</dfn> that implements the interfaces that it
contains.</p>
<p>Conformance requirements phrased as algorithms or specific steps may be
implemented in any manner, so long as the end result is equivalent. (In
particular, the algorithms defined in this specification are intended to be
easy to follow, and not intended to be performant.)</p>
<p>Implementations that use ECMAScript to implement the APIs defined in
this specification MUST implement them in a manner consistent with the
ECMAScript Bindings defined in the Web IDL specification [[WEBIDL]], as
this specification uses that specification and terminology.</p>
</section>
<section>
<h2>Terminology</h2>
<p>
The following terms are defined in
<dfn data-cite="RTP-EXT-CAPTURE-TIME#">RTP Header Extension for Absolute Capture Time</dfn>:
</p>
<ul>
<li><dfn data-cite="RTP-EXT-CAPTURE-TIME#absolute-capture-timestamp">absolute capture timestamp</dfn></li>
<li><dfn data-cite="RTP-EXT-CAPTURE-TIME#timestamp-interpolation">timestamp interpolation</dfn></li>
<li><dfn data-cite="RTP-EXT-CAPTURE-TIME#estimated-capture-clock-offset">estimated capture clock offset</dfn></li>
</ul>
<p>
The process of <dfn data-lt="form|formed|forming">forming</dfn> a candidate pair is defined in
[[RFC8445]] Section 6.1.2.2.
</p>
<p>
The process of <dfn data-lt="nominate|nominated|nomination">nominating</dfn> a candidate pair is defined in
[[RFC8445]] Section 8.1.1.
</p>
<p>
The process of <dfn data-lt="free|freed|freeing">freeing</dfn> a candidate is defined in [[RFC8445]] Section 8.3.
</p>
</section>
<section id="ice-csp">
<h3>
Filtering ICE candidates with Content-Security-Policy
</h3>
<p>
The {{RTCPeerConnection}} interface is defined in [[WEBRTC]]. This document
extends that interface by using Content-Security-Policy for ICE candidate
filtering.
</p>
<section id="ice-csp-modifications">
<h2>Modifications to existing procedures</h2>
<p>Append the following paragraph to the
<a data-cite="WEBRTC#dfn-administratively-prohibited">administratively prohibited</a>
algorithm:</p>
<p>If <a data-cite="CSP#should-block-rtc-connection">
should RTC connections be blocked for global?</a> with the
[=relevant global object=] of the {{RTCPeerConnection}} object in question
returns `"Blocked"`, then all candidates MUST be <a
data-cite="WEBRTC#dfn-administratively-prohibited">
administratively prohibited</a>.</p>
</section>
</section>
<section id="rtp-header-extension-control">
<h2>RTP header extension control</h2>
<p>
RTP header extension control is an extension to {{RTCRtpTransceiver}} that allows
to set and query the RTP header extensions supported and negotiated in SDP.
<p>
The RTP header extension mechanism is defined in [[RFC8285]], with
the SDP negotiation mechanism defined in section 5. It goes into some
detail on the meaning of "direction" with regard to RTP header
extensions, and gives a detailed procedure for negotiating RTP header
extension IDs.
</p>
<p>
This API extension gives the means to control the use and direction of
RTP header extensions as documented in [[RFC8285]]. It does not
influence the ID negotiation mechanism, except for being able to
control the number of extensions offered.
</p>
<section id="rtp-header-extension-control-transceiver-interface">
<h3>
{{RTCRtpTransceiver}} interface extensions
</h3>
<p>
The {{RTCRtpTransceiver}}
interface is defined in [[WEBRTC]]. This document extends that interface
by adding an additional method and attribute in order to control negotiation of
RTP header extensions.
</p>
<pre class="idl">
partial dictionary RTCRtpHeaderExtensionCapability {
required RTCRtpTransceiverDirection direction;
};
partial interface RTCRtpTransceiver {
sequence<RTCRtpHeaderExtensionCapability> getHeaderExtensionsToNegotiate();
undefined setHeaderExtensionsToNegotiate(
sequence<RTCRtpHeaderExtensionCapability> extensions);
sequence<RTCRtpHeaderExtensionCapability> getNegotiatedHeaderExtensions();
};
</pre>
<p>
Let
<dfn data-dfn-for=RTCRtpTransceiver>{{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}}</dfn>
and
<dfn data-dfn-for=RTCRtpTransceiver>{{RTCRtpTransceiver/[[NegotiatedHeaderExtensions]]}}</dfn>
be internal slots of the {{RTCRtpTransceiver}}, initialized as follows:
</p>
<ol>
<li>
<p>Set {{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}} to the
platform-specific list of implemented RTP header extensions. The
{{RTCRtpHeaderExtensionCapability/direction}} attribute for all
extensions that are mandatory to use MUST be initialized to an
appropriate value other than {{RTCRtpTransceiverDirection/"stopped"}}.
The {{RTCRtpHeaderExtensionCapability/direction}} attribute for
extensions that will not be offered by default in an initial offer MUST
be initialized to {{RTCRtpTransceiverDirection/"stopped"}}.</p>
<p class="note">The list of header extensions that MUST/SHOULD be
supported is listed in [[RTCWEB-RTP]], section 5.2. The "mid" extension
is mandatory to use when BUNDLE is in use, per [[BUNDLE]] section
9.1.</p>
</li>
<li>
<p>Set {{RTCRtpTransceiver/[[NegotiatedHeaderExtensions]]}} to an empty
list.</p>
</li>
</ol>
</section>
<section id="rtp-header-extension-control-modifications">
<h2>Modifications to existing procedures</h2>
<p>
Make the following modifications to the
<a data-cite="WEBRTC#set-description">set a session description</a>
algorithm:
</p>
<ul>
<li>
<p>In the step for processing a <var>description</var> of type
{{RTCSdpType/"answer"}} that runs for both local and remote
descriptions, insert the following steps:</p>
<ol>
<li>
<p>For each <var>media description</var> and corresponding
<var>transceiver</var>, let <var>negotiatedExtensions</var> be the
value of
<var>transceiver</var>.{{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}}.</p>
</li>
<li>
<p>For each <var>extension</var> in
<var>negotiatedExtensions</var>, run the following steps:</p>
<ol>
<li>
<p>Let <var>answeredDirection</var> be the direction attribute
of the "a=extmap" line in the answer's
<var>media description</var> that correspond to this
<var>extension</var> if one exists, otherwise set
<var>answeredDirection</var> to
{{RTCRtpTransceiverDirection/"stopped"}}.</p>
</li>
<li>
<p>If <var>description</var> is a remote description, reverse
<var>answeredDirection</var> to represent the peer's point of
view.</p>
</li>
<li>
<p>Set
<var>extension</var>.{{RTCRtpHeaderExtensionCapability/direction}}
to <var>answeredDirection</var>.</p>
</li>
</ol>
</li>
<li>
<p>Set
<var>transceiver</var>.{{RTCRtpTransceiver/[[NegotiatedHeaderExtensions]]}}
to <var>negotiatedExtensions</var>.</p>
</li>
</ol>
</li>
</ul>
<p>
In the algorithms for generating initial offers in [[RTCWEB-JSEP]] section 5.2.1,
replace "for each supported RTP header extension, an "a=extmap" line, as specified in
[[RFC5285]], section 5" " with "For each RTP header extension "e"
listed in {{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}} where {{RTCRtpHeaderExtensionCapability/direction}} is not {{RTCRtpTransceiverDirection/"stopped"}}, an "a=extmap"
line, as specified in [[RFC5285]], section 5, with direction taken from "e"'s {{RTCRtpHeaderExtensionCapability/direction}}
attribute."
</p>
<p>
In the algorithm for generating subsequent offers in [[RTCWEB-JSEP]] section 5.2.2, replace "The
RTP header extensions MUST only include those that are present in the most recent answer"
with "For each RTP header extension listed in {{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}},
and where {{RTCRtpHeaderExtensionCapability/direction}} is not {{RTCRtpTransceiverDirection/"stopped"}}, generate
an appropriate "a=extmap" line with "direction" set according to the rules of [[RFC5285]]
section 6, considering the {{RTCRtpHeaderExtensionCapability/direction}} in {{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}} to indicate the
answerer's desired usage".
</p>
<p>
In the algorithm for generating initial answers in [[RTCWEB-JSEP]] section 5.3.1, replace "For
each supported RTP header extension that is present in the offer" with "For each
supported RTP header extension that is present in the offer and is also present in
{{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}} with a {{RTCRtpHeaderExtensionCapability/direction}} different from {{RTCRtpTransceiverDirection/"stopped"}},
set the appropriate direction based on {{RTCRtpHeaderExtensionCapability/direction}} that does not exceed the direction in the offer".
</p>
<p class="note">
Since JSEP does not know about WebRTC internal slots, merging this change requires
more work on a JSEP revision.
</p>
</section>
<section id="rtp-header-extension-control-transceiver-methods">
<h3>Methods</h3>
<dl>
<dt><dfn data-dfn-for=RTCRtpTransceiver>getHeaderExtensionsToNegotiate</dfn></dt>
<dd>
<p>Execute the following steps:</p>
<ol>
<li>
<p>Let <var>transceiver</var> be the {{RTCRtpTransceiver}} that
this method was invoked on.</p>
</li>
<li>
<p>Return
<var>transceiver</var>.{{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}}.</p>
</li>
</ol>
</dd>
</dl>
<dl>
<dt><dfn data-dfn-for=RTCRtpTransceiver>setHeaderExtensionsToNegotiate</dfn></dt>
<dd>
<p>Execute the following steps:</p>
<ol>
<li>
<p>Let <var>transceiver</var> be the {{RTCRtpTransceiver}} that
this method was invoked on.</p>
</li>
<li>
<p>Let <var>extensions</var> be the first argument of this
method.</p>
</li>
<li>
<p>If the size of <var>extensions</var> does not match the size of
<var>transceiver</var>.{{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}}
[=exception/throw=] an {{InvalidModificationError}}.
</p>
</li>
<li>
<p>For each index <var>i</var> of <var>extensions</var>, run the
following steps:</p>
<ol>
<li>
<p>Let <var>extension</var> be the <var>i</var>-th element of
<var>extensions</var>.</p>
</li>
<li>
<p>If
<var>extension</var>.{{RTCRtpHeaderExtensionCapability/uri}}
is not equal to the {{RTCRtpHeaderExtensionCapability/uri}} of
the <var>i</var>-th element of
<var>transceiver</var>.{{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}},
[=exception/throw=] an {{InvalidModificationError}}.</p>
</li>
<li>
<p>If
<var>extension</var>.{{RTCRtpHeaderExtensionCapability/direction}}
is not {{RTCRtpTransceiverDirection/"sendrecv"}} and
{{RTCRtpHeaderExtensionParameters/uri}} indicates a
mandatory-to-use attribute that is required to be both sent
and received, [=exception/throw=] an
{{InvalidModificationError}}.</p>
</li>
<li>
<p>If
<var>extension</var>.{{RTCRtpHeaderExtensionCapability/direction}}
is {{RTCRtpTransceiverDirection/"stopped"}} and
{{RTCRtpHeaderExtensionCapability/uri}} indicates a
mandatory-to-implement extension, [=exception/throw=] an
{{InvalidModificationError}}.</p>
</li>
<li>
<p>If necessary, restrict
<var>extension</var>.{{RTCRtpHeaderExtensionCapability/direction}}
as to not exceed the user agent's capabilities for this
extension.</p>
</li>
</ol>
</li>
<li>
<p>Set
<var>transceiver</var>.{{RTCRtpTransceiver/[[HeaderExtensionsToNegotiate]]}}
to <var>extensions</var>.</p>
</li>
</ol>
</dd>
</dl>
<dl>
<dt><dfn data-dfn-for=RTCRtpTransceiver>getNegotiatedHeaderExtensions</dfn></dt>
<dd>
<p>Execute the following steps:</p>
<ol>
<li>
<p>Let <var>transceiver</var> be the {{RTCRtpTransceiver}} that
this method was invoked on.</p>
</li>
<li>
<p>Return
<var>transceiver</var>.{{RTCRtpTransceiver/[[NegotiatedHeaderExtensions]]}}.</p>
</li>
</ol>
</dd>
</dl>
</section>
</section>
<section id="rtcrtpencodingparameters">
<h3>
RTCRtpEncodingParameters extensions
</h3>
<p>
The {{RTCRtpEncodingParameters}} dictionary is defined in
[[WEBRTC]]. This document extends that dictionary with
additional members to control audio packetization.
</p>
<pre class="idl">partial dictionary RTCRtpEncodingParameters {
unsigned long ptime;
boolean adaptivePtime = false;
RTCRtpCodec codec;
};</pre>
<section id="rtcrtpencodingparameters-attributes">
<h2>Dictionary {{RTCRtpEncodingParameters}} Members</h2>
<dl data-link-for="RTCRtpEncodingParameters" data-dfn-for="RTCRtpEncodingParameters" class="dictionary-members">
<dt>
<dfn data-idl>ptime</dfn> of type <span class="idlMemberType">unsigned long</span>
</dt>
<dd>
<p>The preferred duration of media represented by a packet in milliseconds.</p>
<div class="issue atrisk">
<p>
{{RTCRtpEncodingParameters/ptime}} was moved from [[WEBRTC]] to
this specification due to lack of support from implementers. It is
therefore marked as a feature at risk.
</p>
</div>
</dd>
<dt>
<dfn data-idl>adaptivePtime</dfn> of type <span class="idlMemberType">boolean</span>,
defaulting to <code>false</code>.
</dt>
<dd>
<p>Indicates whether this encoding MAY dynamically change
the frame length. If the value is <code>true</code>, the
<a>user agent</a> MAY use any valid frame length for any of its
frames, and MAY change this at any time. Valid values are
multiples of 10ms. If the <code>maxptime</code> attribute
(defined in [[RFC4566]] Section 6) is specified, that maximum
applies. If the value is <code>false</code>, the <a>user agent</a>
MUST use a fixed frame length.</p>
<p>If {{adaptivePtime}} is set to <code>true</code>,
{{ptime}} MUST NOT be set; otherwise,
{{InvalidModificationError}} MUST be [=exception/throw|thrown=].</p>
<p class="note">Using a longer frame length reduces the
bandwidth consumption due to overhead, but does so at the cost
of increased latency. Changing the frame length dynamically
allows the <a>user agent</a> to adapt its bandwidth allocation strategy
based on the current network conditions.</p>
</dd>
<dt>
<dfn data-idl>codec</dfn> of type <span class="idlMemberType">RTCRtpCodec</span>
</dt>
<dd>
<p>Optional value selecting which codec is used for this encoding's
RTP stream. The {{RTCRtpCodec}} dictionary is defined in [[WEBRTC]].
If [=map/exists|absent=], the user agent can chose to use any negotiated codec.</p>
</dd>
</dl>
</section>
<section id="rtcrtpencodingparameters-modifications">
<h2>Modifications to existing procedures</h2>
<h3>setParameters()</h3>
<p>Add the following steps to the [=RTCRtpSender/setParameters validation steps=]:</p>
<ol>
<li>
<p>Let <var>choosableCodecs</var> be parameters.{{RTCRtpParameters/codecs}}.</p>
</li>
<li>
<p>If <var>choosableCodecs</var> is an empty list, set <var>choosableCodecs</var>
to transceiver.{{RTCRtpTransceiver/[[PreferredCodecs]]}}.</p>
</li>
<li>
<p>If <var>choosableCodecs</var> is still an empty list, set <var>choosableCodecs</var>
to the [=RTCRtpSender/list of implemented send codecs=] for transceiver's kind.</p>
</li>
<li>
<p>If any <var>encoding</var> in encodings [=map/exists|contains=] a codec
[= codec dictionary match | not found =] in <var>choosableCodecs</var>, return a promise
[= rejected =] with a newly [= exception/created =] {{InvalidModificationError}}.</p>
</li>
<li>
<p>If the user agent does not support setting the codec for any encoding or mixing
different codec values on the different encodings, return a promise [= rejected =]
with a newly [= exception/created =] {{OperationError}}.
</p>
</li>
</ol>
<h3>addTransceiver()</h3>
<p>Add the following steps to the [=RTCPeerConnection/addTransceiver sendEncodings validation steps=]:</p>
<ol>
<li>
<p>If any <var>codec</var> parameter in <var>sendEncodings</var> does [= codec dictionary match | not match =] any codec in
{{RTCRtpSender.getCapabilities(kind)}}.<code>codecs</code>,
[= exception/throw =] an {{OperationError}}.</p>
</li>
<li>
<p>If the user agent does not support changing codecs without negotiation or
does not support setting codecs for individual encodings, return a promise
[= rejected =] with a newly [= exception/created =] {{OperationError}}.</p>
</li>
</ol>
<h3>Set the session description</h3>
<p>Append the following steps to the <a data-cite="WEBRTC#set-description">set the session description</a> algorithm:</p>
<ol>
<li>
<p>For each <var>transceiver</var> in <var>connection</var>'s [= set of transceivers =]:</p>
<ol>
<li>
<p>Let <var>codecs</var> be <var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[SendCodecs]]}}.</p>
</li>
<li>
<p>If <var>codecs</var> is not an empty list:</p>
<ol>
<li>
<p>Remove any <var>codec</var> value in <var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[SendEncodings]]}}
that does not [= codec dictionary match | match =] any entry in <var>codecs</var>.</p>
</li>
</ol>
</li>
</ol>
</li>
</ol>
</section>
</section>
<section id="rtcrtpsender-setparameters-keyframe">
<h3>
{{RTCRtpSender}} {{RTCRtpSender/setParameters()}} extensions for requesting the generation of a key frame.
</h3>
<p>
The {{RTCRtpSender}}'s {{RTCRtpSender/setParameters()}} method is defined in
[[WEBRTC]]. This document extends the optional second argument to request
generation of a key frame by the encoder.
</p>
<pre class="idl">partial dictionary RTCSetParameterOptions {
sequence<RTCEncodingOptions> encodingOptions = [];
};
dictionary RTCEncodingOptions {
boolean keyFrame = false;
};</pre>
<section id="rtcrtpsender-setparameters-keyframe-setparameteroptions-idl">
<h2>Dictionary {{RTCSetParameterOptions}} Members</h2>
<p>
The {{RTCSetParameterOptions}} are extended by a sequence of {{RTCEncodingOptions}}, one for each encoding.
</p>
<dl data-link-for="RTCSetParameterOptions" data-dfn-for="RTCSetParameterOptions" class="dictionary-members">
<dt>
<dfn data-idl>encodingOptions</dfn> of type <span class="idlMemberType">sequence<{{RTCEncodingOptions}}></span>, defaulting to <code>[]</code>.
</dt>
<dd>
<p>
A sequence containing encoding options for each RTP encoding.
</p>
</dd>
</dl>
</section>
<section id="rtcrtpsender-setparameters-keyframe-encodingoptions-idl">
<h2>Dictionary {{RTCEncodingOptions}} Members</h2>
<p>
{{RTCEncodingOptions}} is the WebRTC equivalent of {{VideoEncoderEncodeOptions}} in [[WebCodecs]].
</p>
<dl data-link-for="RTCEncodingOptions" data-dfn-for="RTCEncodingOptions" class="dictionary-members">
<dt>
<dfn data-idl>keyFrame</dfn> of type <span class="idlMemberType">boolean</span>, defaulting to <code>false</code>.
</dt>
<dd>
<p>
When set to true, request that RTCRtpSender's encoder generates a keyframe for the encoding.
The semantic of this boolean is similar to the RTCP FIR message described in [RFC5104], section 3.5.1.
</p>
</dd>
</dl>
</section>
<section id="rtcrtpsender-setparameters-keyframe-interface-extensions">
<h2>{{RTCRtpSender}} {{RTCRtpSender/setParameters()}} modifications to existing procedures</h2>
<p>
In the steps to call the {{RTCRtpSender/setParameters()}} method,
let <var>parameters</var> be the method's first argument and let
<var>setParameterOptions</var> be the method's second argument.
</p>
<p>Append the following steps after the steps to validate the <var>parameters</var>:</p>
<ul>
<li>
<p>If the [=RTCRtpTransceiver/transceiver kind=] of the associated kind is `"audio"`, set
<var>setParameterOptions.encodingOptions</var> to the empty list.</p>
</li>
<li>
<p>If <var>setParameterOptions.encodingOptions</var> is not empty and
<code><var>setParameterOptions.encodingOptions</var>.length</code> is
different from <code><var>parameters</var>.encodings.length</code>,
return a promise [= rejected =] with a newly [= exception/created =] {{InvalidModificationError}}.</p>
</li>
</ul>
<p>In the steps to configure the media stack to use <var>parameters</var>, append the following step:</p>
<ul>
<li>
<p>For each <var>setParameterOptions.encodingOptions</var> indexed by <var>i</var>,
if <code><var>setParameterOptions.encodingOptions</var>[i].keyFrame</code> is set to <code>true</code>,
request that the encoder associated with <code><var>parameters</var>.encodings[i]</code> generates a key frame.</p>
</li>
</ul>
<p class="note">
{{RTCRtpSender/setParameters()}} does not wait for a key frame to be produced by the encoder.
</p>
</section>
</section>
<section id="rtcicetransport">
<h3>
{{RTCIceTransport}} extensions
</h3>
<p>
The {{RTCIceTransport}} interface is defined in [[WEBRTC]]. This document extends that interface to allow an
application to observe and affect certain actions that an <dfn>ICE agent</dfn> [[RFC5245]] performs.
</p>
<p>
The [= ICE agent =] performs connectivity checks to identify valid candidate pairs on which it is possible to send
and receive media and data. In order to conclude ICE processing, the [= ICE agent =] {{nominates}} a valid candidate
pair as the selected candidate pair. Prior to nomination, any valid candidate pair may be used to send and receive data.
Once
a candidate pair is nominated successfully, only the selected candidate pair will be used to send and receive data.
Changing
the selected candidate pair after a successful nomination requires an ICE restart.
</p>
<p>
When the [= ICE agent =] has [= formed =] a candidate pair, the [= user agent =] MUST [= queue a task =] to <dfn
id="rtcicetransport-add">add a candidate pair</dfn>:
</p>
<ol class="algorithm">
<li>
<p>
Let |connection:RTCPeerConnection| be the {{RTCPeerConnection}} object associated with this [= ICE agent =].
</p>
</li>
<li>
<p>
If <var>connection</var>.{{RTCPeerConnection/[[IsClosed]]}} is
<code>true</code>, abort these steps.
</p>
</li>
<li>
<p>
Let |candidatePair:RTCIceCandidatePair| be a new {{RTCIceCandidatePair}} dictionary
with its {{RTCIceCandidatePair/local}} and {{RTCIceCandidatePair/remote}} members
initialized to new {{RTCIceCandidate}}s representing the local and remote part of the
[= formed =] pair respectively.
</p>
</li>
<li>
<p>
Let |transport:RTCIceTransport| be the {{RTCIceTransport}} object associated with |candidatePair|.
</p>
</li>
<li>
<p>
[=Assert=]: |candidatePair| does not [= candidate pair match | match =] any
item in |transport|.{{RTCIceTransport/[[CandidatePairs]]}}
</p>
</li>
<li>
<p>
[= list/Append =] |candidatePair| to {{RTCIceTransport/[[CandidatePairs]]}}.
</p>
</li>
<li>
<p>
[= Fire an event =] named
{{RTCIceTransport/icecandidatepairadd}} at |transport|, using {{RTCIceCandidatePairEvent}},
with the {{RTCIceCandidatePairEvent/local}} and {{RTCIceCandidatePairEvent/remote}} attributes
initialized to the local and remote candidates, respectively, of |candidatePair|.
</p>
</li>
</ol>
<p>
When the [= ICE agent =] has picked a candidate pair to {{nominate}} as the selected candidate pair, the [= user
agent =]
MUST [= queue a task =] to <dfn id="rtcicetransport-nominate" data-lt="nominate the candidate pair">nominate a
candidate pair</dfn>:
</p>
<ol class="algorithm">
<li>
<p>
Let |connection:RTCPeerConnection| be the {{RTCPeerConnection}} object associated with this [= ICE agent =].
</p>
</li>
<li>
<p>
If <var>connection</var>.{{RTCPeerConnection/[[IsClosed]]}} is
<code>true</code>, abort these steps.
</p>
</li>
<li>
<p>
Let |transport:RTCIceTransport| be the {{RTCIceTransport}} object associated with this candidate pair.
</p>
</li>
<li>
<p>
Let |candidatePair:RTCIceCandidatePair| be the candidate pair which is being {{nominated}}.
</p>
</li>
<li>
<p>
Set |transport|.{{RTCIceTransport/[[ProposalPending]]}} to <code>true</code>.
</p>
</li>
<li>
<p>
Let |accepted:boolean| be the result of [= fire an event | firing an event =] named
{{RTCIceTransport/icecandidatepairnominate}} at |transport|, using {{RTCIceCandidatePairEvent}}, with the
{{Event/cancelable}} attribute initialized to <code>true</code>, and the {{RTCIceCandidatePairEvent/local}} and
{{RTCIceCandidatePairEvent/remote}} attributes initialized to the local and remote candidates, respectively, of
|candidatePair|.
</p>
</li>
<li>
<p>
Set |transport|.{{RTCIceTransport/[[ProposalPending]]}} to <code>false</code>.
</p>
</li>
<li>
<p>
If |accepted| is <code>false</code>, abort these steps and instruct the [= ICE agent =] to continue to perform connectivity checks.
</p>
</li>
<li>
<p>
Otherwise, instruct the [= ICE agent =] to {{nominate}} the candidate pair indicated by |candidatePair|.
</p>
</li>
</ol>
<p class="note">
The [= ICE agent =] will continue to send data using |candidatePair| until instructed to use another candidate pair with {{RTCIceTransport/selectCandidatePair}}.
</p>
<p>
When the [= ICE agent =] has picked a candidate pair to remove, the [= user agent =] MUST [= queue a task =] to <dfn
id="rtcicetransport-remove">remove a candidate pair</dfn>:
</p>
<ol class="algorithm">
<li>
<p>
Let |connection:RTCPeerConnection| be the {{RTCPeerConnection}} object associated with this [= ICE agent =].
</p>
</li>
<li>
<p>
If <var>connection</var>.{{RTCPeerConnection/[[IsClosed]]}} is
<code>true</code>, abort these steps.
</p>
</li>
<li>
<p>
Let |candidatePair:RTCIceCandidatePair| be the candidate pair which is being removed.
</p>
</li>
<li>
<p>
Let |transport:RTCIceTransport| be the {{RTCIceTransport}} object associated with |candidatePair|.
</p>
</li>
<li>
<p>
Let |cancelable:boolean| be <code>true</code> if the candidate pair is being removed in order to [= free =] an unused
candidate, and
<code>false</code> otherwise.
</p>
</li>
<li>
<p>
Set |transport|.{{RTCIceTransport/[[ProposalPending]]}} to <code>true</code>.
</p>
</li>
<li>
<p>
Let |accepted:boolean| be the result of [= fire an event | firing an event =] named
{{RTCIceTransport/icecandidatepairremove}} at |transport|, using {{RTCIceCandidatePairEvent}}, with the
{{Event/cancelable}} attribute initialized to <var>cancelable</var>, and the {{RTCIceCandidatePairEvent/local}}
and {{RTCIceCandidatePairEvent/remote}} attributes initialized to the local and remote candidates, respectively,
of |candidatePair|.
</p>
</li>
<li>
<p>
Set |transport|.{{RTCIceTransport/[[ProposalPending]]}} to <code>false</code>.
</p>
</li>
<li>
<p>
If |accepted| is <code>false</code>, instruct the [= ICE agent =] to not remove the candidate pair indicated by
|candidatePair|, and instead continue to send and respond to ICE connectivity checks on the candidate pair as
before.
</p>
</li>
<li>
<p>
Otherwise (if |accepted| is <code>true</code>), run the following steps:
</p>
<ol>
<li>
<p>
[= list/Remove =] |candidatePair| from |transport|.{{RTCIceTransport/[[CandidatePairs]]}}.
</p>
</li>
<li>
<p>
Instruct the [= ICE agent =] to remove the candidate pair indicated by |candidatePair|.
</p>
</li>
</ol>
</li>
</ol>
<p>
The {{RTCIceTransport}} object is extended by adding the following internal slots:
</p>
<ul>
<li>
<dfn data-dfn-for="RTCIceTransport">[[\CandidatePairs]]</dfn> initialized to an empty list.
</li>
<li>
<dfn data-dfn-for="RTCIceTransport">[[\ProposalPending]]</dfn> initialized to <code>false</code>.
</li>
</ul>
<pre class="idl">
partial interface RTCIceTransport {
attribute EventHandler onicecandidatepairadd;
attribute EventHandler onicecandidatepairremove;
attribute EventHandler onicecandidatepairnominate;
Promise<undefined> selectCandidatePair(RTCIceCandidatePair candidatePair);
Promise<undefined> removeCandidatePair(RTCIceCandidatePair candidatePair);
};</pre>
<section id="rtcicetransport-attributes">
<h2>Attributes</h2>
<dl data-link-for="RTCIceTransport" data-dfn-for="RTCIceTransport" class="attributes">
<dt>
<dfn>onicecandidatepairadd</dfn> of type <span class="idlAttrType">{{EventHandler}}</span>
</dt>
<dd>
<p>
The event type of this event handler is {{icecandidatepairadd}}, and is fired as part of
the [= add a candidate pair =] algorithm.
</p>
</dd>
<dt>
<dfn>onicecandidatepairremove</dfn> of type <span class="idlAttrType">{{EventHandler}}</span>
</dt>
<dd>
<p>
The event type of this event handler is {{icecandidatepairremove}}, and is fired as part of
the [= remove a candidate pair =] algorithm.
</p>
</dd>
<dt>
<dfn>onicecandidatepairnominate</dfn> of type <span class="idlAttrType">{{EventHandler}}</span>
</dt>
<dd>
<p>
The event type of this event handler is {{icecandidatepairnominate}}, and is fired as part
of the [= nominate a candidate pair =] algorithm.
</p>
</dd>
</dl>
</section>
<section id="rtcicetransport-methods">
<h2>Methods</h2>
<dl data-link-for="RTCIceTransport" data-dfn-for="RTCIceTransport" class="methods">
<dt>
<dfn>selectCandidatePair</dfn>
</dt>
<dd>
<p>
The {{selectCandidatePair}} method attempts to select a different candidate pair to send data
over. If successful, data will be sent on the provided candidate pair.
It is meant to be called after the application defers the {{nomination}} of a candidate pair
by cancelling the {{RTCIceTransport/icecandidatepairnominate}} event.
<p>
<p>
When this method is invoked, the [= user agent =] MUST run the following steps:
</p>
<ol class="algorithm">
<li>
<p>
Let |connection:RTCPeerConnection| be the {{RTCPeerConnection}} object associated with [=this=].
</p>
</li>
<li>
<p>
If <var>connection</var>.{{RTCPeerConnection/[[IsClosed]]}} is
<code>true</code>, [= exception/throw =] an {{InvalidStateError}}.
</p>
</li>
<li>
<p>
If [=this=].{{RTCIceTransport/[[ProposalPending]]}} is <code>true</code>, [= exception/throw =] an {{InvalidStateError}}.
</p>
</li>
<li>
<p>
If [=this=].{{RTCIceTransport/[[IceTransportState]]}} is either of
{{RTCIceTransportState/"new"}}, {{RTCIceTransportState/"failed"}} or {{RTCIceTransportState/"closed"}}, [=
exception/throw =]
an {{InvalidStateError}}.
</p>
</li>
<li>
<p>
Let |candidatePair:RTCIceCandidatePair| be the method's first argument.
</p>
</li>
<li>
<p>
If |candidatePair| does not [= candidate pair match | match =] any item in [=this=].
{{RTCIceTransport/[[CandidatePairs]]}}, [= exception/throw =] a {{NotFoundError}}.
</p>
</li>
<li>
<p>
Let |p:Promise| be a new promise.
</p>
</li>
<li>
<p>
In parallel, instruct the [= ICE agent =] to use |candidatePair| to send data.
</p>
<ol>
<li>
<p>
When the [= ICE agent =] has completed selecting |candidatePair|, [= queue a task =] to run the following steps:
</p>
<ol>
<li>
<p>
Run the [=RTCIceTransport/change the selected candidate pair and state=] steps to update [=this=].{{RTCIceTransport/[[SelectedCandidatePair]]}} and [=this=].{{RTCIceTransport/[[IceTransportState]]}} as necessary and fire any associated events.
</p>
</li>
<li>
<p>
Resolve <var>p</var>.
</p>
</li>
</ol>
</li>
</ol>
</li>
<li>
<p>
Return <var>p</var>.
</p>
</li>
</ol>
<p class="note">
After changing the selected candidate pair, the controlling [= ICE agent =] may attempt to [= nominate the candidate
pair =] as
well to conclude ICE processing. The application may cancel the nomination to allow further changes to the selected
candidate pair.
</p>
</dd>
<dt>
<dfn>removeCandidatePair</dfn>
</dt>
<dd>
<p>
The {{removeCandidatePair}} method removes the provided candidate pair. The [= ICE agent =] will stop sending and
responding to ICE connectivity checks on the removed candidate pair, and it can no longer be used to send data for this
transport. This method is meant to be called when the application wants to allow the [= ICE agent =] to [= free =]
candidates that it no longer needs.
</p>
<p>
When this method is invoked, the [= user agent =] MUST run the following steps:
</p>
<ol class="algorithm">
<li>
<p>
Let |connection:RTCPeerConnection| be the {{RTCPeerConnection}} object associated with [= this =].
</p>
</li>
<li>
<p>
If <var>connection</var>.{{RTCPeerConnection/[[IsClosed]]}} is
<code>true</code>, [= exception/throw =] an
{{InvalidStateError}}.
</p>
</li>
<li>
<p>
If [= this =].{{RTCIceTransport/[[ProposalPending]]}} is <code>true</code>, [= exception/throw =] an
{{InvalidStateError}}.
</p>
</li>
<li>
<p>
If [= this =].{{RTCIceTransport/[[IceTransportState]]}} is either of {{RTCIceTransportState/"new"}}, {{RTCIceTransportState/"failed"}} or {{RTCIceTransportState/"closed"}}, [= exception/throw =] an {{InvalidStateError}}.
</p>
</li>
<li>
<p>
Let |candidatePair:RTCIceCandidatePair| be the method's first argument.
</p>
</li>
<li>
<p>
If |candidatePair| does not [= candidate pair match | match =] any item in [=this=].
{{RTCIceTransport/[[CandidatePairs]]}}, [= exception/throw =] a {{NotFoundError}}.
</p>
</li>
<li>
<p>
[= list/Remove =] the item in
[=this=].{{RTCIceTransport/[[CandidatePairs]]}} that
[= candidate pair match | matches =] |candidatePair|.
</p>
</li>
<li>
<p>
Let |p:Promise| be a new promise.
</p>
</li>
<li>
<p>
In parallel, instruct the [= ICE agent =] to remove the candidate pair indicated by <var>candidatePair</var>.
</p>
<ol>
<li>
<p>
When the [= ICE agent =] has completed the removal, [= queue a task =] to run the following steps:
</p>
<ol>
<li>
<p>
[= Fire an event =] named {{RTCIceTransport/icecandidatepairremove}} at |transport|, using {{RTCIceCandidatePairEvent}}, with the {{Event/cancelable}} attribute initialized to <code>false</code>, and the {{RTCIceCandidatePairEvent/local}} and {{RTCIceCandidatePairEvent/remote}} attributes initialized to the {{RTCIceCandidatePair/local}} and {{RTCIceCandidatePair/remote}} candidates, respectively, of <var>candidatePair</var>.
</p>
</li>
<li>
<p>
Resolve <var>p</var>.
</p>
</li>
</ol>
</li>
</ol>
</li>
<li>
<p>
Return <var>p</var>.
</p>
</li>
</ol>
</dd>