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Merge pull request #2758 from jan-ivar/norescaledown
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Don't let offers to receive simulcast overwrite existing [[SendEncodings]]
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@alvestrand
alvestrand authored Oct 13, 2022
2 parents f8565ce + 561937b commit d183990
Showing 1 changed file with 58 additions and 31 deletions.
89 changes: 58 additions & 31 deletions webrtc.html
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Original file line number Diff line number Diff line change
Expand Up @@ -1758,21 +1758,35 @@ <h4>
<li>
<p id="remote-rid-reneg">
If <var>remote</var> is <code>true</code>, and
<var>description</var> is of type {{RTCSdpType/"offer"}}
and contains a request to receive simulcast, and applying
<var>description</var> leads to modifying a
transceiver <var>transceiver</var>, and
<var>description</var> is of type
{{RTCSdpType/"offer"}}, then for each
[= media description =] requesting to receive simulcast
that already has an existing {{RTCRtpTransceiver}} object,
<var>transceiver</var>, associated with it, as described in
<span data-jsep="applying-a-remote-desc">[[!RFC8829]]</span>,
if none of the encodings in
<var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[SendEncodings]]}}
is non-empty, and not equal to the encodings that would
result from processing <var>description</var>, the
process of applying <var>description</var> fails. This
specification does not allow remotely initiated RID
renegotiation.
[=map/contain=] a {{RTCRtpCodingParameters/rid}} member
whose value matches any of the rids in the simulcast
attribute, then [= description fails | fail =] the
process of applying <var>description</var>.
<div class="note">
A change in rids values is tolerated in remote offers to
receive simulcast as long as at least one rid matches a
rid in the encodings that were previously negotiated, or
the offer is to no longer receive simulcast.
Mismatched or out-of-order rids result in layer removal,
and layer expansion is prevented in user agent answers.
This specification does not allow remotely initiated RID
renegotiation.
</div>
</p>
</li>
<li>
<p>
If the process to apply <var>description</var> fails for
If the <dfn data-lt="description fails"
id="fail-description">process to apply
<var>description</var> fails</dfn> for
any reason, then the user agent MUST queue a task that
runs the following steps:
</p>
Expand Down Expand Up @@ -2322,32 +2336,33 @@ <h4>
<li>
<p>
If the <var>description</var> is of type
{{RTCSdpType/"offer"}} and contains a request
{{RTCSdpType/"offer"}} and the
[= media description =] contains a request
to receive simulcast, use the order of the
rid values specified in the simulcast
attribute to create an
{{RTCRtpEncodingParameters}} dictionary for
each of the simulcast layers, populating the
{{RTCRtpCodingParameters/rid}} 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.
let <var>proposedSendEncodings</var> be the
list containing the created dictionaries.
Otherwise, let <var>proposedSendEncodings</var>
be an empty list.
</p>
</li>
<li>Let <var>supportedEncodings</var> be the
maximum number of encodings that the
implementation can support. If the length of
<var>sendEncodings</var> is greater than
<var>proposedSendEncodings</var> is greater than
<var>supportedEncodings</var>, truncate
<var>sendEncodings</var> so that its length is
<var>proposedSendEncodings</var> so that its length is
<var>supportedEncodings</var>.
</li>
<li>If <var>sendEncodings</var> is non-empty, set
each encoding's
<li>If <var>proposedSendEncodings</var> is non-empty,
set each encoding's
{{RTCRtpEncodingParameters/scaleResolutionDownBy}}
to <code>2^(length of <var>sendEncodings</var> -
to <code>2^(length of <var>proposedSendEncodings</var> -
encoding index - 1)</code>.
</li>
<li>
Expand All @@ -2363,13 +2378,25 @@ <h4>
<li>
<p>
If a suitable transceiver was found
(<var>transceiver</var> is set) and
<var>sendEncodings</var> is non-empty, set
<var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[SendEncodings]]}}
to <var>sendEncodings</var>, and set
<var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[LastReturnedParameters]]}}
to <code>null</code>.
(<var>transceiver</var> is set), and
<var>proposedSendEncodings</var> is non-empty,
run the following steps:
</p>
<ol>
<li class="needs-test">
<p>
If the length of
<var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[SendEncodings]]}}
is `1`, and the lone encoding
[=map/contains=] no
{{RTCRtpCodingParameters/rid}} member, set
<var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[SendEncodings]]}}
to <var>proposedSendEncodings</var>, and set
<var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[LastReturnedParameters]]}}
to <code>null</code>.
</p>
</li>
</ol>
</li>
<li>
<p>
Expand All @@ -2384,7 +2411,7 @@ <h4>
[= Create an RTCRtpSender =],
<var>sender</var>, from the [= media
description =] using
<var>sendEncodings</var>.
<var>proposedSendEncodings</var>.
</p>
</li>
<li data-tests=
Expand Down Expand Up @@ -2440,10 +2467,10 @@ <h4>
</li>
<li>
<p>
If <var>description</var> rejects any of
the offered layers, then remove the
dictionaries that correspond to rejected
layers from
If <var>description</var> is missing any of
the previously negototiated layers, then
remove the dictionaries that correspond to
the missing layers from
<var>transceiver</var>.{{RTCRtpTransceiver/[[Sender]]}}.{{RTCRtpSender/[[SendEncodings]]}}.
</p>
</li>
Expand Down

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