From da7e6eeb190ace108edf7dd988297b4abdcedfde Mon Sep 17 00:00:00 2001
From: David Zhao <dz@livekit.io>
Date: Fri, 15 Mar 2024 01:11:30 -0700
Subject: [PATCH] a couple of fixups

---
 src/room/PCTransport.ts                  | 34 ++++++++++++++++++++++++
 src/room/participant/LocalParticipant.ts |  7 ++---
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/src/room/PCTransport.ts b/src/room/PCTransport.ts
index 52748b5b4..ca92ba325 100644
--- a/src/room/PCTransport.ts
+++ b/src/room/PCTransport.ts
@@ -267,6 +267,40 @@ export default class PCTransport extends EventEmitter {
         ensureAudioNackAndStereo(media, [], []);
       } else if (media.type === 'video') {
         ensureVideoDDExtensionForSVC(media);
+        // mung sdp for codec bitrate setting that can't apply by sendEncoding
+        this.trackBitrates.some((trackbr): boolean => {
+          if (!media.msid || !trackbr.cid || !media.msid.includes(trackbr.cid)) {
+            return false;
+          }
+
+          let codecPayload = 0;
+          media.rtp.some((rtp): boolean => {
+            if (rtp.codec.toUpperCase() === trackbr.codec.toUpperCase()) {
+              codecPayload = rtp.payload;
+              return true;
+            }
+            return false;
+          });
+
+          if (codecPayload === 0) {
+            return true;
+          }
+
+          const startBitrate = Math.round(trackbr.maxbr * startBitrateForSVC);
+
+          for (const fmtp of media.fmtp) {
+            if (fmtp.payload === codecPayload) {
+              // if another track's fmtp already is set, we cannot override the bitrate
+              // this has the unfortunate consequence of being forced to use the
+              // initial track's bitrate for all tracks
+              if (!fmtp.config.includes('x-google-start-bitrate')) {
+                fmtp.config += `;x-google-start-bitrate=${startBitrate}`;
+              }
+              break;
+            }
+          }
+          return true;
+        });
       }
     });
 
diff --git a/src/room/participant/LocalParticipant.ts b/src/room/participant/LocalParticipant.ts
index 6f7c224df..f3dc9adb2 100644
--- a/src/room/participant/LocalParticipant.ts
+++ b/src/room/participant/LocalParticipant.ts
@@ -732,7 +732,7 @@ export default class LocalParticipant extends Participant {
       // for svc codecs, disable simulcast and use vp8 for backup codec
       if (track instanceof LocalVideoTrack) {
         if (isSVCCodec(videoCodec)) {
-          if (track.source === Track.Source.ScreenShare && videoCodec === 'vp9') {
+          if (track.source === Track.Source.ScreenShare) {
             // vp9 svc with screenshare cannot encode multiple spatial layers
             // doing so reduces publish resolution to minimal resolution
             opts.scalabilityMode = 'L1T3';
@@ -743,7 +743,7 @@ export default class LocalParticipant extends Participant {
             // that we need
             if ('contentHint' in track.mediaStreamTrack) {
               track.mediaStreamTrack.contentHint = 'motion';
-              this.log.info('forcing contentHint to motion for screenshare with VP9', {
+              this.log.info('forcing contentHint to motion for screenshare with SVC codecs', {
                 ...this.logContext,
                 ...getLogContextFromTrack(track),
               });
@@ -881,7 +881,8 @@ export default class LocalParticipant extends Participant {
             maxbr: encodings[0]?.maxBitrate ? encodings[0].maxBitrate / 1000 : 0,
           });
         }
-      } else if (track.codec && isSVCCodec(track.codec) && encodings[0]?.maxBitrate) {
+      } else if (track.codec && track.codec == 'av1' && encodings[0]?.maxBitrate) {
+        // AV1 requires setting x-start-bitrate in SDP
         this.engine.pcManager.publisher.setTrackCodecBitrate({
           cid: req.cid,
           codec: track.codec,