fix(ScreenObtainer): Apply contentHint on captured desktop track correctly.

contentHint needs to be set to 'motion' for high fps SS and 'detail' otherwise. Fixes https://github.com/jitsi/lib-jitsi-meet/issues/2298.

JitsiMeetJS.ts

@@ -334,15 +334,6 @@ export default {
                     }
                 }
 
-                // set the contentHint to "detail" for desktop tracks
-                // eslint-disable-next-line prefer-const
-                for (const track of tracks) {
-                    if (track.type === MediaType.VIDEO
-                        && track.videoType === 'desktop') {
-                        this.setVideoTrackContentHints(track.track, 'detail');
-                    }
-                }
-
                 return tracks;
             })
             .catch(error => {
@@ -531,24 +522,6 @@ export default {
         NetworkInfo.updateNetworkInfo({ isOnline });
     },
 
-    /**
-     * Set the contentHint on the transmitted stream track to indicate
-     * charaterstics in the video stream, which informs PeerConnection
-     * on how to encode the track (to prefer motion or individual frame detail)
-     * @param {MediaStreamTrack} track - the track that is transmitted
-     * @param {String} hint - contentHint value that needs to be set on the track
-     */
-    setVideoTrackContentHints(track, hint) {
-        if ('contentHint' in track) {
-            track.contentHint = hint;
-            if (track.contentHint !== hint) {
-                logger.debug('Invalid video track contentHint');
-            }
-        } else {
-            logger.debug('MediaStreamTrack contentHint attribute not supported');
-        }
-    },
-
     precallTest,
 
     /* eslint-enable max-params */

modules/RTC/ScreenObtainer.js

@@ -180,11 +180,15 @@ const ScreenObtainer = {
 
                         // We have to use the old API on Electron to get a desktop stream.
                         navigator.mediaDevices.getUserMedia(constraints)
-                            .then(stream => onSuccess({
-                                stream,
-                                sourceId: streamId,
-                                sourceType: streamType
-                            }), onFailure);
+                            .then(stream => {
+                                this.setContentHint(stream);
+                                onSuccess({
+                                    stream,
+                                    sourceId: streamId,
+                                    sourceType: streamType
+                                });
+                            })
+                            .catch(err => onFailure(err));
                     } else {
                         // As noted in Chrome Desktop Capture API:
                         // If user didn't select any source (i.e. canceled the prompt)
@@ -257,6 +261,7 @@ const ScreenObtainer = {
 
         getDisplayMedia(constraints)
             .then(stream => {
+                this.setContentHint(stream);
                 callback({
                     stream,
                     sourceId: stream.id
@@ -294,6 +299,7 @@ const ScreenObtainer = {
 
         navigator.mediaDevices.getDisplayMedia({ video: true })
             .then(stream => {
+                this.setContentHint(stream);
                 callback({
                     stream,
                     sourceId: stream.id });
@@ -304,6 +310,24 @@ const ScreenObtainer = {
             });
     },
 
+    /** Sets the contentHint on the transmitted MediaStreamTrack to indicate charaterstics in the video stream, which
+     * informs RTCPeerConnection on how to encode the track (to prefer motion or individual frame detail).
+     *
+     * @param {MediaStream} stream - The captured desktop stream.
+     * @returns {void}
+     */
+    setContentHint(stream) {
+        const { desktopSharingFrameRate } = this.options;
+        const desktopTrack = stream.getVideoTracks()[0];
+
+        // Set contentHint on the desktop track based on the fps requested.
+        if ('contentHint' in desktopTrack) {
+            desktopTrack.contentHint = desktopSharingFrameRate?.max > SS_DEFAULT_FRAME_RATE ? 'motion' : 'detail';
+        } else {
+            logger.warn('MediaStreamTrack contentHint attribute not supported');
+        }
+    },
+
     /**
      * Sets the max frame rate to be used for a desktop track capture.
      *

types/hand-crafted/JitsiMeetJS.d.ts

@@ -137,8 +137,6 @@ export type JitsiMeetJSType = {
 
   setNetworkInfo: ( { isOnline: boolean } ) => void;
 
-  setVideoTrackContentHints: ( track: MediaStreamTrack, hint: string ) => void;
-
   precallTest: PrecallTest;
 
   util: {