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Define remote track settings, constraints not applicable #2340

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Define remote track settings, constraints not applicable #2340

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Define remote track settings, constraints not applicable
henbos Oct 24, 2019
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henbos Oct 24, 2019
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henbos Oct 31, 2019
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71 changes: 58 additions & 13 deletions webrtc.html
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Expand Up @@ -11725,19 +11725,64 @@ <h3 id="mediastreamtrack-network-use">MediaStreamTrack</h3>
<section>
<h4>MediaTrackSupportedConstraints, MediaTrackCapabilities,
MediaTrackConstraints and MediaTrackSettings</h4>
<p>The basics of <code>MediaTrackSupportedConstraints</code>,
<code>MediaTrackCapabilites</code>, <code>MediaTrackConstraints</code>
and <code>MediaTrackSettings</code> is outlined in [[!GETUSERMEDIA]].
However, the <code>MediaTrackSettings</code> for a
<code>MediaStreamTrack</code> sourced by an
<code><a>RTCPeerConnection</a></code> will only be populated with
members to the extent that data is supplied by means of the remote
<code><a>RTCSessionDescription</a></code> applied via
<code>setRemoteDescription</code> and the actual RTP data. This means
that certain members, such as <code>facingMode</code>,
<code>echoCancellation</code>, <code>latency</code>,
<code>deviceId</code> and <code>groupId</code>, will always be
missing.</p>
<p>The concept of constraints and constrainable properties, including
<code>MediaTrackConstraints</code>
(<code>MediaStreamTrack.getConstraints()</code>,
<code>MediaStreamTrack.applyConstraints()</code>), and
<code>MediaTrackSettings</code>
(<code>MediaStreamTrack.getSettings()</code>) are outlined in
[[!GETUSERMEDIA]]. However, the constrainable properties of tracks
sourced from a peer connection are different than those sourced by
<code>getUserMedia()</code>; the constraints and settings applicable to
<code><a>MediaStreamTrack</a></code>s sourced from a <a>remote
source</a> are defined here. The settings of a remote track represent
the latest frame received.
<code>MediaStreamTrack.getCapabilities()</code> MUST always return the
empty set and <code>MediaStreamTrack.applyConstraints()</code> MUST
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always reject with <code>OverconstrainedError</code> on remote tracks
for constraints defined here.</p>
<p>The following constrainable properties are defined to apply to video
<code><a>MediaStreamTrack</a></code>s sourced from a <a>remote
source</a>:</p>
<table class="simple">
<thead>
<tr>
<th>Property Name</th>
<th>Values</th>
<th>Notes</th>
</tr>
</thead>
<tbody>
<tr id="def-constraint-width">
<td><dfn>width</dfn></td>
<td><code>ConstrainULong</code></td>
<td>As a setting, this is the width, in pixels, of the latest
frame received.</td>
</tr>
<tr id="def-constraint-height">
<td><dfn>height</dfn></td>
<td><code>ConstrainULong</code></td>
<td>As a setting, this is the height, in pixels, of the latest
frame received.</td>
</tr>
<tr id="def-constraint-frameRate">
<td><dfn>frameRate</dfn></td>
<td><code>ConstrainDouble</code></td>
<td>As a setting, this is an estimate of the frame rate based on
recently received frames.</td>
</tr>
<tr id="def-constraint-aspect">
<td><dfn>aspectRatio</dfn></td>
<td><code>ConstrainDouble</code></td>
<td>As a setting, this is the aspect ratio of the latest frame;
this is the width in pixels divided by height in pixels as a
double rounded to the tenth decimal place.</td>
</tr>
</tbody>
</table>
<p>This document does not define any constrainable properties to apply
to audio <code><a>MediaStreamTrack</a></code>s sourced from a <a>remote
source</a>.</p>
</section>
</section>
</section>
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