fix(FF): Don't add recvonly SSRC in session-accept

modules/RTC/TraceablePeerConnection.js

@@ -256,6 +256,19 @@ export default function TraceablePeerConnection(
     this._usesTransceiverCodecPreferences
         && logger.info('Using RTCRtpTransceiver#setCodecPreferences for codec selection');
 
+    // We currently need these flags only for FF and that's why we are updating them only for unified plan.
+    if (this._usesUnifiedPlan) {
+        /**
+         * Indicates whether an audio track has ever been added to the peer connection.
+         */
+        this._hasHadAudioTrack = false;
+
+        /**
+         * Indicates whether a video track has ever been added to the peer connection.
+         */
+        this._hasHadAudioTrack = false;
+    }
+
     /**
      * @type {number} The max number of stats to keep in this.stats. Limit to
      * 300 values, i.e. 5 minutes; set to 0 to disable
@@ -1672,6 +1685,13 @@ TraceablePeerConnection.prototype.addTrack = function(track, isInitiator = false
         logger.debug(`${this} TPC.addTrack using unified plan`);
         try {
             this.tpcUtils.addTrack(track, isInitiator);
+            if (track) {
+                if (track.isAudioTrack()) {
+                    this._hasHadAudioTrack = true;
+                } else {
+                    this._hasHadVideoTrack = true;
+                }
+            }
         } catch (error) {
             logger.error(`${this} Adding track=${track} failed: ${error?.message}`);
 
@@ -1753,7 +1773,17 @@ TraceablePeerConnection.prototype.addTrackUnmute = function(track) {
     }
 
     if (this._usesUnifiedPlan) {
-        return this.tpcUtils.replaceTrack(null, track).then(() => false);
+        return this.tpcUtils.replaceTrack(null, track).then(() => {
+            if (track) {
+                if (track.isAudioTrack()) {
+                    this._hasHadAudioTrack = true;
+                } else {
+                    this._hasHadVideoTrack = true;
+                }
+            }
+
+            return false;
+        });
     }
 
     this._addStream(webRtcStream);
@@ -1985,6 +2015,14 @@ TraceablePeerConnection.prototype.replaceTrack = function(oldTrack, newTrack) {
 
         return promise
             .then(transceiver => {
+                if (newTrack) {
+                    if (newTrack.isAudioTrack()) {
+                        this._hasHadAudioTrack = true;
+                    } else {
+                        this._hasHadVideoTrack = true;
+                    }
+                }
+
                 oldTrack && this.localTracks.delete(oldTrack.rtcId);
                 newTrack && this.localTracks.set(newTrack.rtcId, newTrack);
 

modules/sdp/LocalSdpMunger.js

@@ -4,6 +4,7 @@ import { MediaDirection } from '../../service/RTC/MediaDirection';
 import { MediaType } from '../../service/RTC/MediaType';
 import { getSourceNameForJitsiTrack } from '../../service/RTC/SignalingLayer';
 import { VideoType } from '../../service/RTC/VideoType';
+import browser from '../browser';
 import FeatureFlags from '../flags/FeatureFlags';
 
 import { SdpTransformWrap } from './SdpTransformUtil';
@@ -245,8 +246,28 @@ export default class LocalSdpMunger {
             return;
         }
 
-        // Add the msid attribute if it is missing when the direction is sendrecv/sendonly. Firefox doesn't produce a
-        // a=ssrc line with msid attribute for p2p connection.
+        const mediaDirection = mediaSection.mLine?.direction;
+
+        // On FF when the user has started muted create answer will generate a recv only SSRC. We don't want to signal
+        // this SSRC in order to reduce the load of the xmpp server for large calls. Therefore the SSRC needs to be
+        // removed from the SDP.
+        //
+        // For all other use cases (when the user has had media but then the user has stopped it) we want to keep the
+        // receive only SSRCs in the SDP. Otherwise source-remove will be triggered and the next time the user add a
+        // track we will reuse the SSRCs and send source-add with the same SSRCs. This is problematic because of issues
+        // on Chrome and FF (https://bugzilla.mozilla.org/show_bug.cgi?id=1768729) when removing and then adding the
+        // same SSRC in the remote sdp the remote track is not rendered.
+        if (browser.isFirefox()
+            && (mediaDirection === MediaDirection.RECVONLY || mediaDirection === MediaDirection.INACTIVE)
+            && (
+                (mediaType === MediaType.VIDEO && !this.tpc._hadVideoAdded)
+                || (mediaType === MediaType.AUDIO && !this.tpc._hadAudioAdded)
+            )
+        ) {
+            mediaSection.ssrcs = undefined;
+            mediaSection.ssrcGroups = undefined;
+        }
+
         const msidLine = mediaSection.mLine?.msid;
         const trackId = msidLine && msidLine.split(' ')[1];
         const sources = [ ...new Set(mediaSection.mLine?.ssrcs?.map(s => s.id)) ];

types/auto/modules/RTC/TraceablePeerConnection.d.ts

@@ -229,6 +229,10 @@ export default class TraceablePeerConnection {
      * munging for codec selection.
      */
     _usesTransceiverCodecPreferences: boolean;
+    /**
+     * Indicates whether an audio track has ever been added to the peer connection.
+     */
+    _hasHadAudioTrack: boolean;
     /**
      * @type {number} The max number of stats to keep in this.stats. Limit to
      * 300 values, i.e. 5 minutes; set to 0 to disable
@@ -495,6 +499,7 @@ export default class TraceablePeerConnection {
      * @returns {Promise<void>} - resolved when done.
      */
     addTrack(track: any, isInitiator?: boolean): Promise<void>;
+    _hasHadVideoTrack: boolean;
     /**
      * Adds local track as part of the unmute operation.
      * @param {JitsiLocalTrack} track the track to be added as part of the unmute operation.