Clarify comment on previous fix (#1838)

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 ### Changed
+- Clarified comment in `DefaultSimulcastUplinkPolicy`.
 
 ## [2.23.0] - 2021-11-22
 ### Added

docs/classes/defaultsimulcastuplinkpolicy.html

@@ -235,7 +235,7 @@ <h3>add<wbr>Observer</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#addobserver">addObserver</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L388">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:388</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L395">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:395</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-parameters-title">Parameters</h4>
@@ -259,7 +259,7 @@ <h3>choose<wbr>Capture<wbr>And<wbr>Encode<wbr>Parameters</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#choosecaptureandencodeparameters">chooseCaptureAndEncodeParameters</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L292">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:292</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L299">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:299</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-returns-title">Returns <span class="tsd-signature-type">DefaultVideoAndEncodeParameter</span></h4>
@@ -277,7 +277,7 @@ <h3>choose<wbr>Encoding<wbr>Parameters</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#chooseencodingparameters">chooseEncodingParameters</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L202">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:202</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L209">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:209</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-returns-title">Returns <span class="tsd-signature-type">Map</span><span class="tsd-signature-symbol">&lt;</span><span class="tsd-signature-type">string</span><span class="tsd-signature-symbol">, </span><span class="tsd-signature-type">RTCRtpEncodingParameters</span><span class="tsd-signature-symbol">&gt;</span></h4>
@@ -295,7 +295,7 @@ <h3>choose<wbr>Media<wbr>Track<wbr>Constraints</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#choosemediatrackconstraints">chooseMediaTrackConstraints</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L191">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:191</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L198">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:198</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-returns-title">Returns <span class="tsd-signature-type">MediaTrackConstraints</span></h4>
@@ -312,7 +312,7 @@ <h3>for<wbr>Each<wbr>Observer</h3>
 						<li class="tsd-description">
 							<aside class="tsd-sources">
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L398">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:398</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L405">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:405</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-parameters-title">Parameters</h4>
@@ -353,7 +353,7 @@ <h3>get<wbr>Encoding<wbr>Simulcast<wbr>Layer</h3>
 						<li class="tsd-description">
 							<aside class="tsd-sources">
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L366">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:366</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L373">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:373</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-parameters-title">Parameters</h4>
@@ -377,7 +377,7 @@ <h3>max<wbr>Bandwidth<wbr>Kbps</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#maxbandwidthkbps">maxBandwidthKbps</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L315">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:315</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L322">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:322</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-returns-title">Returns <span class="tsd-signature-type">number</span></h4>
@@ -395,7 +395,7 @@ <h3>remove<wbr>Observer</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#removeobserver">removeObserver</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L393">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:393</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L400">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:400</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-parameters-title">Parameters</h4>
@@ -419,7 +419,7 @@ <h3>set<wbr>Has<wbr>Bandwidth<wbr>Priority</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#sethasbandwidthpriority">setHasBandwidthPriority</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L324">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:324</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L331">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:331</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-parameters-title">Parameters</h4>
@@ -443,7 +443,7 @@ <h3>set<wbr>Ideal<wbr>Max<wbr>Bandwidth<wbr>Kbps</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#setidealmaxbandwidthkbps">setIdealMaxBandwidthKbps</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L320">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:320</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L327">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:327</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-parameters-title">Parameters</h4>
@@ -495,7 +495,7 @@ <h3>update<wbr>Index</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#updateindex">updateIndex</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L212">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:212</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L219">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:219</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-parameters-title">Parameters</h4>
@@ -519,7 +519,7 @@ <h3>wants<wbr>Resubscribe</h3>
 							<aside class="tsd-sources">
 								<p>Implementation of <a href="../interfaces/simulcastuplinkpolicy.html">SimulcastUplinkPolicy</a>.<a href="../interfaces/simulcastuplinkpolicy.html#wantsresubscribe">wantsResubscribe</a></p>
 								<ul>
-									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L239">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:239</a></li>
+									<li>Defined in <a href="https://github.com/aws/amazon-chime-sdk-js/blob/master/src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts#L246">src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts:246</a></li>
 								</ul>
 							</aside>
 							<h4 class="tsd-returns-title">Returns <span class="tsd-signature-type">boolean</span></h4>

src/videouplinkbandwidthpolicy/DefaultSimulcastUplinkPolicy.ts

@@ -136,14 +136,21 @@ export default class DefaultSimulcastUplinkPolicy implements SimulcastUplinkPoli
         // The value of `newActiveStreams` is somewhat irrelevant since this single
         // stream will adapt based on both sender and receiver network conditions.
         //
-        // We don't use top layer (middle vs. low doesn't matter) here to work around a bug in Chromium where
+        // We use middle layer here to work around a bug in Chromium where
         // it seems when a transceiver is created when BWE is low (e.g. on a reconnection),
         // it will never reset the encoder even when `setParameters` is called.  WebRTC bug
         // #12788 seems to call a similar issue out as fixed for VP8, it's not clear if this
         // is the same issue for H.264. Additionally we are not able to force a keyframe
         // request from the backend since it will only be sending padding (which also
         // don't have MID due to #10822). Since we don't scale when simulcast is disabled
         // this doesn't have any end-user effect.
+        //
+        // Note that this still relies on a little bit (5-6 packets) of padding on reconnect
+        // and that technically the browser will still eventually try to send all 3 streams.
+        //
+        // Also note that due to some uninvestigated logic in bitrate allocation, Chromium
+        // will skip the bottom layer if we try setting it to 1200 kbps instead so it will still take a while to
+        // recover (as it needs to send padding until it reaches around 1000 kbps).
         this.newActiveStreams = ActiveStreams.kHi;
         newBitrates[0].maxBitrateKbps = 0;
         newBitrates[1].maxBitrateKbps = 1200;