From f9ea07e43c3bab8b8a4d54dfc189ac71df9a651c Mon Sep 17 00:00:00 2001
From: David Baker <dbkr@users.noreply.github.com>
Date: Thu, 13 Jun 2024 14:11:48 +0100
Subject: [PATCH 1/3] 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.
---
 src/webrtc/call.ts | 42 +++++++++++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 45d35f60c9f..723c0108c68 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -25,7 +25,7 @@ import { v4 as uuidv4 } from "uuid";
 import { parse as parseSdp, write as writeSdp } from "sdp-transform";
 
 import { logger } from "../logger";
-import { checkObjectHasKeys, isNullOrUndefined, recursivelyAssign } from "../utils";
+import { checkObjectHasKeys, deepCompare, isNullOrUndefined, recursivelyAssign } from "../utils";
 import { MatrixEvent } from "../models/event";
 import { EventType, TimelineEvents, ToDeviceMessageId } from "../@types/event";
 import { RoomMember } from "../models/room-member";
@@ -2381,22 +2381,42 @@ 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);
+        //screenshareVideoTransceiver.setCodecPreferences(codecs);
     }
 
     private onNegotiationNeeded = async (): Promise<void> => {

From 81d7430ca7eeb0133ff3e4a67c0501c4926ecc4f Mon Sep 17 00:00:00 2001
From: David Baker <dbkr@users.noreply.github.com>
Date: Thu, 13 Jun 2024 14:17:47 +0100
Subject: [PATCH 2/3] Unused import

---
 src/webrtc/call.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 723c0108c68..27dc578d89b 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -25,7 +25,7 @@ import { v4 as uuidv4 } from "uuid";
 import { parse as parseSdp, write as writeSdp } from "sdp-transform";
 
 import { logger } from "../logger";
-import { checkObjectHasKeys, deepCompare, isNullOrUndefined, recursivelyAssign } from "../utils";
+import { checkObjectHasKeys, isNullOrUndefined, recursivelyAssign } from "../utils";
 import { MatrixEvent } from "../models/event";
 import { EventType, TimelineEvents, ToDeviceMessageId } from "../@types/event";
 import { RoomMember } from "../models/room-member";

From f97308cbc4071dbb58ac97f1ed8c49d08c49463e Mon Sep 17 00:00:00 2001
From: David Baker <dbkr@users.noreply.github.com>
Date: Thu, 13 Jun 2024 14:20:39 +0100
Subject: [PATCH 3/3] Remove commented line

---
 src/webrtc/call.ts | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 27dc578d89b..3f5c61a9e23 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -2415,8 +2415,6 @@ export class MatrixCall extends TypedEventEmitter<CallEvent, CallEventHandlerMap
                 }
             }
         }
-
-        //screenshareVideoTransceiver.setCodecPreferences(codecs);
     }
 
     private onNegotiationNeeded = async (): Promise<void> => {