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Clarifying how the simulcast envelope is created. #2081

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Feb 14, 2019
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Clarifying how the simulcast envelope is created. #2081

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d90cd0e
Clarifying how the simulcast envelope is created.
amithilbuch Jan 22, 2019
8d76314
Changing the specified behavior when simulcast or layers are rejected.
amithilbuch Feb 7, 2019
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45 changes: 44 additions & 1 deletion webrtc.html
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Original file line number Diff line number Diff line change
Expand Up @@ -1750,9 +1750,19 @@ <h4>Set the RTCSessionDescription</h4>
(<var>transceiver</var> is unset), run the following
steps:</p>
<ol>
<li>
<p>If the <var>description</var> is of type <code>"offer"</code>
and contains a request to receive simulcast, follow the order
of the rid values specified in the simulcast attribute to create
an <code><a>RTCRtpEncodingParameters</a></code> dictionary for
each of the simulcast layers, populating the <a>rid</a> member
according to the corresponding rid value, and let <var>sendEncodings</var>
be the list containing the created dictionaries.
Otherwise, let <var>sendEncodings</var> be an empty list.</p>
</li>
<li>
<p><a>Create an RTCRtpSender</a>, <var>sender</var>,
from the <a>media description</a>.</p>
from the <a>media description</a> using <var>sendEncodings</var>.</p>
</li>
<li>
<p><a>Create an RTCRtpReceiver</a>,
Expand All @@ -1767,6 +1777,33 @@ <h4>Set the RTCSessionDescription</h4>
</li>
</ol>
</li>
<li>
<p>If <var>description</var> is of type <code>"answer"</code>
or <code>"pranswer"</code>, and <var>transceiver</var>.
<a>[[\Sender]]</a>.<a>[[\sendEncodings]]</a> .length is
greater than <code>1</code>, then run the following steps:</p>
<ol>
<li>
<p>If <var>description</var> indicates that simulcast is
not supported or desired, then remove all dictionaries in
<var>transceiver</var>.<a>[[\Sender]]</a>.<a>[[\sendEncodings]]</a>
except the first one and abort these sub steps.</p>
</li>
<li>
<p>If <var>description</var> rejects any of the offered layers,
then remove the dictionaries that correspond to rejected layers from
<var>transceiver</var>.<a>[[\Sender]]</a>.<a>[[\sendEncodings]]</a>.</p>
</li>
<li>
<p>Update the paused status as indicated by [[MMUSIC-SIMULCAST]] of
each simulcast layer by setting the
<code><a data-link-for="RTCRtpEncodingParameters">active</a></code>
member on the corresponding dictionaries in
<var>transceiver</var>.<a>[[\Sender]]</a>.<a>[[\sendEncodings]]</a>
to <code>true</code> for unpaused or to <code>false</code> for paused.</p>
</li>
</ol>
</li>
<li>
<p>Set <var>transceiver</var>'s <code><a data-link-for=
"RTCRtpTransceiver">mid</a></code> value to the mid of
Expand Down Expand Up @@ -7604,6 +7641,12 @@ <h3>Simulcast functionality</h3>
implications of this model is that the <code>addTrack</code> method cannot provide simulcast
functionality since it does not take <code>sendEncodings</code> as an argument, and therefore cannot
configure an <code><a>RTCRtpTransceiver</a></code> to send simulcast.</p>
<p>Another implication is that the answerer cannot set the <a>simulcast envelope</a> directly.
Upon calling the <code>setRemoteDescription</code> method of the <code><a>RTCPeerConnection</a></code>
object, the <a>simulcast envelope</a> is configured on the <code><a>RTCRtpTransceiver</a></code>
to contain the layers described by the specified <code><a>RTCSessionDescription</a></code>.
Once the envelope is determined, layers cannot be removed. They can be marked as inactive by setting
the <code>active</code> attribute to <code>false</code> effectively disabling the layer.</p>
<p>While <code>setParameters</code> cannot modify the <a>simulcast envelope</a>, it is still possible
to control the number of streams that are sent and the characteristics of those streams. Using
<code>setParameters</code>, simulcast streams can be made inactive by setting the <code>active</code>
Expand Down