From 9218f6380ce6ddd3944e9d945a0887d007df9d4d Mon Sep 17 00:00:00 2001
From: David Baker <dbkr@users.noreply.github.com>
Date: Thu, 13 Jun 2024 19:44:30 +0100
Subject: [PATCH] Fix screen sharing in recent Chrome (#4241)

* Fix screen sharing in recent Chrome

Dreadful hack to work around a bug in recent chrome/electron's
WebRTC, as explained.

I'm not sure which is the least hideous out of this (ie. repeatedly
calling setCodecPreferences and seeing if it crashes each time) or
hardcoding the bad codec and skipping it. Opinions welcome.

* Unused import

* Remove commented line
---
 src/webrtc/call.ts | 42 ++++++++++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 45d35f60c..3f5c61a9e 100644
--- 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 recvCodecs = RTCRtpReceiver.getCapabilities("video")!.codecs;
-        const sendCodecs = RTCRtpSender.getCapabilities("video")!.codecs;
-        const codecs = [...sendCodecs, ...recvCodecs];
-
-        for (const codec of codecs) {
-            if (codec.mimeType === "video/rtx") {
-                const rtxCodecIndex = codecs.indexOf(codec);
-                codecs.splice(rtxCodecIndex, 1);
-            }
-        }
-
         const screenshareVideoTransceiver = this.transceivers.get(
             getTransceiverKey(SDPStreamMetadataPurpose.Screenshare, "video"),
         );
+
         // setCodecPreferences isn't supported on FF (as of v113)
-        screenshareVideoTransceiver?.setCodecPreferences?.(codecs);
+        if (!screenshareVideoTransceiver || !screenshareVideoTransceiver.setCodecPreferences) return;
+
+        const recvCodecs = RTCRtpReceiver.getCapabilities("video")!.codecs;
+        const sendCodecs = RTCRtpSender.getCapabilities("video")!.codecs;
+        const codecs = [];
+
+        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();
+                }
+            }
+        }
     }
 
     private onNegotiationNeeded = async (): Promise<void> => {