change: apply codec preferences via native browser API

CHANGELOG.md

@@ -15,6 +15,10 @@ Added new telemetry events to enhance monitoring and diagnostics for the followi
 - [RTCIceGatheringState](https://w3c.github.io/webrtc-pc/#rtcicegatheringstate-enum)
 - [RTCIceConnectionState](https://w3c.github.io/webrtc-pc/#rtciceconnectionstate-enum)
 
+Changes
+-------
+- Replaced SDP munging for codec preferences with native `RTCRtpTransceiver.setCodecPreferences()` API.
+
 2.33.0 (November 6, 2025)
 ====================
 

lib/signaling/v2/peerconnection.js

@@ -23,11 +23,9 @@ const {
   createCodecMapForMediaSection,
   disableRtx,
   enableDtxForOpus,
-  filterLocalCodecs,
   getMediaSections,
   removeSSRCAttributes,
   revertSimulcast,
-  setCodecPreferences,
   setSimulcast
 } = require('../../util/sdp');
 
@@ -40,7 +38,6 @@ const {
 
 const {
   buildLogLevels,
-  getPlatform,
   isChromeScreenShareTrack,
   oncePerTick,
   defer
@@ -57,8 +54,6 @@ const workaroundIssue8329 = require('../../util/sdp/issue8329');
 const telemetry = require('../../insights/telemetry');
 
 const guess = util.guessBrowser();
-const platform = getPlatform();
-const isAndroid = /android/.test(platform);
 const isChrome = guess === 'chrome';
 const isFirefox = guess === 'firefox';
 const isSafari = guess === 'safari';
@@ -125,7 +120,6 @@ class PeerConnectionV2 extends StateMachine {
       offerOptions: {},
       revertSimulcast,
       sessionTimeout: DEFAULT_SESSION_TIMEOUT_SEC * 1000,
-      setCodecPreferences,
       setSimulcast,
       Backoff: DefaultBackoff,
       IceConnectionMonitor: DefaultIceConnectionMonitor,
@@ -149,7 +143,10 @@ class PeerConnectionV2 extends StateMachine {
     }
 
     const log = options.log ? options.log.createLog('webrtc', this) : new Log('webrtc', this, logLevels, options.loggerName);
-    const peerConnection = new RTCPeerConnection(configuration, options.chromeSpecificConstraints);
+    const peerConnection = new RTCPeerConnection(configuration, {
+      chromeSpecificConstraints: options.chromeSpecificConstraints,
+      applyCodecPreferences: transceiver => this._applyCodecPreferencesToTransceiver(transceiver)
+    });
 
     if (options.dummyAudioMediaStreamTrack) {
       peerConnection.addTrack(options.dummyAudioMediaStreamTrack);
@@ -326,15 +323,6 @@ class PeerConnectionV2 extends StateMachine {
         writable: true,
         value: new IceBox()
       },
-      _setCodecPreferences: {
-        // NOTE(mmalavalli): Re-ordering payload types in order to make sure a non-H264
-        // preferred codec is selected does not work on Android Firefox due to this behavior:
-        // https://bugzilla.mozilla.org/show_bug.cgi?id=1683258. So, we work around this by
-        // not applying any non-H264 preferred video codec.
-        value: isFirefox && isAndroid && preferredCodecs.video[0] && preferredCodecs.video[0].codec.toLowerCase() !== 'h264'
-          ? sdp => sdp
-          : options.setCodecPreferences
-      },
       _setSimulcast: {
         value: options.setSimulcast
       },
@@ -586,6 +574,67 @@ class PeerConnectionV2 extends StateMachine {
     return Promise.all(candidates.map(this._addIceCandidate, this)).then(() => {});
   }
 
+  /**
+   * Apply codec preferences to a transceiver.
+   * @private
+   * @param {RTCRtpTransceiver} transceiver
+   * @returns {void}
+   */
+  _applyCodecPreferencesToTransceiver(transceiver) {
+    if (!transceiver || !transceiver.receiver || !transceiver.receiver.track) {
+      return;
+    }
+
+    const kind = transceiver.receiver.track.kind;
+    const preferredCodecs = kind === 'audio'
+      ? this._preferredAudioCodecs
+      : this._preferredVideoCodecs;
+
+    if (!preferredCodecs || preferredCodecs.length === 0) {
+      return;
+    }
+
+    try {
+      const availableCodecs = RTCRtpReceiver.getCapabilities(kind).codecs;
+      const sortedCodecs = this._sortCodecsByPreference(availableCodecs, preferredCodecs);
+      transceiver.setCodecPreferences(sortedCodecs);
+    } catch (error) {
+      this._log.warn('Failed to apply codec preferences:', error);
+    }
+  }
+
+  /**
+   * Sort codecs by preference.
+   * @private
+   * @param {Array} availableCodecs
+   * @param {Array} preferredCodecs
+   * @returns {Array}
+   */
+  _sortCodecsByPreference(availableCodecs, preferredCodecs) {
+    const preferred = [];
+    const remaining = [];
+
+    const preferredNames = preferredCodecs.map(c =>
+      (typeof c === 'string' ? c : c.codec).toLowerCase()
+    );
+
+    availableCodecs.forEach(codec => {
+      const codecName = codec.mimeType.split('/')[1].toLowerCase();
+      const index = preferredNames.indexOf(codecName);
+
+      if (index >= 0) {
+        if (!preferred[index]) {
+          preferred[index] = [];
+        }
+        preferred[index].push(codec);
+      } else {
+        remaining.push(codec);
+      }
+    });
+
+    return preferred.flat().concat(remaining);
+  }
+
   /**
    * Add a new RTCRtpTransceiver or update an existing RTCRtpTransceiver for the
    * given MediaStreamTrack.
@@ -613,7 +662,9 @@ class PeerConnectionV2 extends StateMachine {
       return transceiver;
     }
     // NOTE(lrivas): The second argument {} is optional in the specification but required by the Citrix VDI implementations.
-    return this._peerConnection.addTransceiver(track, {});
+    const newTransceiver = this._peerConnection.addTransceiver(track, {});
+    this._applyCodecPreferencesToTransceiver(newTransceiver);
+    return newTransceiver;
   }
 
   /**
@@ -1046,6 +1097,8 @@ class PeerConnectionV2 extends StateMachine {
     }
 
     return Promise.all(this._replaceTrackPromises.values()).then(() => {
+      const transceivers = this._peerConnection.getTransceivers();
+      transceivers.forEach(transceiver => this._applyCodecPreferencesToTransceiver(transceiver));
       return this._peerConnection.createOffer(offerOptions);
     }).catch(error => {
       const errorToThrow = new MediaClientLocalDescFailedError();
@@ -1073,15 +1126,7 @@ class PeerConnectionV2 extends StateMachine {
       // and PSA: https://groups.google.com/forum/#!searchin/discuss-webrtc/PSA%7Csort:date/discuss-webrtc/jcZO-Wj0Wus/k2XvPCvoAwAJ
       // Looks like we are not referencing those attributes, but this changes goes ahead and removes them to see if it works.
       // this also helps reduce bytes on wires
-      let sdp = removeSSRCAttributes(offer.sdp, ['mslabel', 'label']);
-      sdp = this._peerConnection.remoteDescription
-        ? filterLocalCodecs(sdp, this._peerConnection.remoteDescription.sdp)
-        : sdp;
-
-      let updatedSdp = this._setCodecPreferences(
-        sdp,
-        this._preferredAudioCodecs,
-        this._preferredVideoCodecs);
+      let updatedSdp = removeSSRCAttributes(offer.sdp, ['mslabel', 'label']);
 
       this._shouldOffer = false;
       if (!this._negotiationRole) {
@@ -1226,11 +1271,6 @@ class PeerConnectionV2 extends StateMachine {
    */
   _setRemoteDescription(description) {
     if (description.sdp) {
-      description.sdp = this._setCodecPreferences(
-        description.sdp,
-        this._preferredAudioCodecs,
-        this._preferredVideoCodecs);
-
       if (this._shouldApplyDtx) {
         description.sdp = enableDtxForOpus(description.sdp);
       } else {