From d25b86caf40290310bfbc328f84e175e775dcf1f Mon Sep 17 00:00:00 2001
From: cnderrauber <zengjie9004@gmail.com>
Date: Tue, 12 Jul 2022 09:24:12 +0800
Subject: [PATCH] mung sdp for av1 bitrate setting (#314)

* mung sdp for av1 bitrate setting

* code clean

* Update src/room/participant/LocalParticipant.ts

Co-authored-by: lukasIO <mail@lukasseiler.de>

* Update src/room/participant/LocalParticipant.ts

Co-authored-by: lukasIO <mail@lukasseiler.de>

Co-authored-by: lukasIO <mail@lukasseiler.de>
---
 .changeset/lemon-ads-smoke.md            |  5 +++
 src/room/PCTransport.ts                  | 39 ++++++++++++++++++++++++
 src/room/participant/LocalParticipant.ts | 15 +++++++++
 src/room/participant/publishUtils.ts     |  2 +-
 4 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/lemon-ads-smoke.md

diff --git a/.changeset/lemon-ads-smoke.md b/.changeset/lemon-ads-smoke.md
new file mode 100644
index 0000000000..32168b27ac
--- /dev/null
+++ b/.changeset/lemon-ads-smoke.md
@@ -0,0 +1,5 @@
+---
+'livekit-client': patch
+---
+
+apply av1 bitrate setting
diff --git a/src/room/PCTransport.ts b/src/room/PCTransport.ts
index bec2a1f48d..0b51adafde 100644
--- a/src/room/PCTransport.ts
+++ b/src/room/PCTransport.ts
@@ -1,6 +1,13 @@
 import { debounce } from 'ts-debounce';
 import log from '../logger';
 
+/** @internal */
+interface TrackBitrateInfo {
+  sid: string;
+  codec: string;
+  maxbr: number;
+}
+
 /** @internal */
 export default class PCTransport {
   pc: RTCPeerConnection;
@@ -11,6 +18,8 @@ export default class PCTransport {
 
   renegotiate: boolean = false;
 
+  trackBitrates: TrackBitrateInfo[] = [];
+
   onOffer?: (offer: RTCSessionDescriptionInit) => void;
 
   constructor(config?: RTCConfiguration) {
@@ -78,10 +87,40 @@ export default class PCTransport {
     // actually negotiate
     log.debug('starting to negotiate');
     const offer = await this.pc.createOffer(options);
+
+    // mung sdp for codec bitrate setting that can't apply by sendEncoding
+    this.trackBitrates.forEach((trackbr) => {
+      let sdp = offer.sdp ?? '';
+      const sidIndex = sdp.search(new RegExp(`msid.* ${trackbr.sid}`));
+      if (sidIndex < 0) {
+        return;
+      }
+
+      const mlineStart = sdp.substring(0, sidIndex).lastIndexOf('m=');
+      const mlineEnd = sdp.indexOf('m=', sidIndex);
+      const mediaSection = sdp.substring(mlineStart, mlineEnd);
+
+      const mungedMediaSection = mediaSection.replace(
+        new RegExp(`a=rtpmap:(\\d+) ${trackbr.codec}/\\d+`, 'i'),
+        `$&\r\na=fmtp:$1 x-google-max-bitrate=${trackbr.maxbr}`,
+      );
+      sdp = sdp.substring(0, mlineStart) + mungedMediaSection + sdp.substring(mlineEnd);
+      offer.sdp = sdp;
+    });
+    this.trackBitrates = [];
+
     await this.pc.setLocalDescription(offer);
     this.onOffer(offer);
   }
 
+  setTrackCodecBitrate(sid: string, codec: string, maxbr: number) {
+    this.trackBitrates.push({
+      sid,
+      codec,
+      maxbr,
+    });
+  }
+
   close() {
     this.pc.close();
   }
diff --git a/src/room/participant/LocalParticipant.ts b/src/room/participant/LocalParticipant.ts
index 47aca3feef..5f732ce9c7 100644
--- a/src/room/participant/LocalParticipant.ts
+++ b/src/room/participant/LocalParticipant.ts
@@ -544,6 +544,14 @@ export default class LocalParticipant extends Participant {
       track.codec = opts.videoCodec;
     }
 
+    if (track.codec === 'av1' && encodings && encodings[0]?.maxBitrate) {
+      this.engine.publisher.setTrackCodecBitrate(
+        req.cid,
+        track.codec,
+        encodings[0].maxBitrate / 1000,
+      );
+    }
+
     this.engine.negotiate();
 
     // store RTPSender
@@ -642,6 +650,13 @@ export default class LocalParticipant extends Participant {
     this.setPreferredCodec(transceiver, track.kind, opts.videoCodec);
     track.setSimulcastTrackSender(opts.videoCodec, transceiver.sender);
 
+    if (videoCodec === 'av1' && encodings[0]?.maxBitrate) {
+      this.engine.publisher.setTrackCodecBitrate(
+        req.cid,
+        videoCodec,
+        encodings[0].maxBitrate / 1000,
+      );
+    }
     this.engine.negotiate();
     log.debug(`published ${opts.videoCodec} for track ${track.sid}`, { encodings, trackInfo: ti });
   }
diff --git a/src/room/participant/publishUtils.ts b/src/room/participant/publishUtils.ts
index 9f1ed77789..6dc5a03eff 100644
--- a/src/room/participant/publishUtils.ts
+++ b/src/room/participant/publishUtils.ts
@@ -106,7 +106,7 @@ export function computeVideoEncodings(
           encodings.push({
             rid: videoRids[2 - i],
             scaleResolutionDownBy: 2 ** i,
-            maxBitrate: videoEncoding ? videoEncoding.maxBitrate / 2 ** i : 0,
+            maxBitrate: videoEncoding ? videoEncoding.maxBitrate / 3 ** i : 0,
             /* @ts-ignore */
             maxFramerate: original.encoding.maxFramerate,
             /* @ts-ignore */