Fix FPS and latency bugs with VP9 screenshare. (#1069)

* Fix FPS and latency bugs with VP9 screenshare.

Also restored L3T3_KEY publishing for screen share. It was disabled previously.

Chrome does not allow more than 5 fps with L1T3, and it has encoding bugs with L3T3
It has a different path for screenshare handling and it seems to be untested/buggy
As a workaround, we are setting contentHint to force it to go through the same
path as regular camera video. While this is not optimal, it delivers the performance
that we need

* changeset

* added info log when contentHint is overridden

.changeset/smooth-glasses-jam.md

@@ -0,0 +1,5 @@
+---
+"livekit-client": patch
+---
+
+Fix FPS and latency issues with VP9 screenshare

src/room/participant/LocalParticipant.ts

@@ -734,7 +734,20 @@ export default class LocalParticipant extends Participant {
         if (isSVCCodec(videoCodec)) {
           // vp9 svc with screenshare has problem to encode, always use L1T3 here
           if (track.source === Track.Source.ScreenShare && videoCodec === 'vp9') {
-            opts.scalabilityMode = 'L1T3';
+            // Chrome does not allow more than 5 fps with L1T3, and it has encoding bugs with L3T3
+            // It has a different path for screenshare handling and it seems to be untested/buggy
+            // As a workaround, we are setting contentHint to force it to go through the same
+            // path as regular camera video. While this is not optimal, it delivers the performance
+            // that we need
+            if ('contentHint' in track.mediaStreamTrack) {
+              track.mediaStreamTrack.contentHint = 'motion';
+              this.log.info('forcing contentHint to motion for screenshare with VP9', {
+                ...this.logContext,
+                ...getLogContextFromTrack(track),
+              });
+            } else {
+              opts.scalabilityMode = 'L1T3';
+            }
           }
           // set scalabilityMode to 'L3T3_KEY' by default
           opts.scalabilityMode = opts.scalabilityMode ?? 'L3T3_KEY';

src/room/track/RemoteAudioTrack.ts

@@ -1,6 +1,6 @@
 import { TrackEvent } from '../events';
-import { computeBitrate } from '../stats';
 import type { AudioReceiverStats } from '../stats';
+import { computeBitrate } from '../stats';
 import type { LoggerOptions } from '../types';
 import { isReactNative, supportsSetSinkId } from '../utils';
 import RemoteTrack from './RemoteTrack';