[Backport staging] Fix screen sharing in recent Chrome (#4243)

Co-authored-by: David Baker <[email protected]>
matrix-org · Jun 13, 2024 · 2ee43ca · 2ee43ca
1 parent 395c3cf
commit 2ee43ca
Showing 1 changed file with 29 additions and 11 deletions.
diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
@@ -2381,22 +2381,40 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
         // RTCRtpReceiver.getCapabilities and RTCRtpSender.getCapabilities don't seem to be supported on FF before v113
         if (!RTCRtpReceiver.getCapabilities || !RTCRtpSender.getCapabilities) return;
 
+        const screenshareVideoTransceiver = this.transceivers.get(
+            getTransceiverKey(SDPStreamMetadataPurpose.Screenshare, "video"),
+        );
+
+        // setCodecPreferences isn't supported on FF (as of v113)
+        if (!screenshareVideoTransceiver || !screenshareVideoTransceiver.setCodecPreferences) return;
+
         const recvCodecs = RTCRtpReceiver.getCapabilities("video")!.codecs;
         const sendCodecs = RTCRtpSender.getCapabilities("video")!.codecs;
-        const codecs = [...sendCodecs, ...recvCodecs];
+        const codecs = [];
 
-        for (const codec of codecs) {
-            if (codec.mimeType === "video/rtx") {
-                const rtxCodecIndex = codecs.indexOf(codec);
-                codecs.splice(rtxCodecIndex, 1);
+        for (const codec of [...recvCodecs, ...sendCodecs]) {
+            if (codec.mimeType !== "video/rtx") {
+                codecs.push(codec);
+                try {
+                    screenshareVideoTransceiver.setCodecPreferences(codecs);
+                } catch (e) {
+                    // Specifically, Chrome around version 125 and Electron 30 (which is Chromium 124) return an H.264 codec in
+                    // the sender's capabilities but throw when you try to set it. Hence... this mess.
+                    // Specifically, that codec is:
+                    // {
+                    //   clockRate: 90000,
+                    //   mimeType: "video/H264",
+                    //   sdpFmtpLine: "level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=640034",
+                    // }
+                    logger.info(
+                        "Working around buggy WebRTC impl: claimed to support codec but threw when setting codec preferences",
+                        codec,
+                        e,
+                    );
+                    codecs.pop();
+                }
             }
         }
-
-        const screenshareVideoTransceiver = this.transceivers.get(
-            getTransceiverKey(SDPStreamMetadataPurpose.Screenshare, "video"),
-        );
-        // setCodecPreferences isn't supported on FF (as of v113)
-        screenshareVideoTransceiver?.setCodecPreferences?.(codecs);
     }
 
     private onNegotiationNeeded = async (): Promise<void> => {