Signal new tracks explicitly.

client.go

@@ -353,6 +353,8 @@ func addUpConn(c *client, id string) (*upConnection, error) {
 			rate:       estimator.New(time.Second),
 			jitter:     jitter.New(remote.Codec().ClockRate),
 			maxBitrate: ^uint64(0),
+			localCh:    make(chan struct{}, 2),
+			writerDone: make(chan struct{}),
 		}
 		u.tracks = append(u.tracks, track)
 		var tracks []*upTrack
@@ -432,20 +434,18 @@ func readLoop(conn *upConnection, track *upTrack) {
 }
 
 func writeLoop(conn *upConnection, track *upTrack, ch <-chan packetIndex) {
-	var localTime uint64
-	var local []*downTrack
+	defer close(track.writerDone)
 
 	buf := make([]byte, packetcache.BufSize)
 	var packet rtp.Packet
 
-	for {
-		now := mono.Microseconds()
-		if now < localTime || now > localTime+500000 {
-			local = track.getLocal()
-			localTime = now
-		}
+	local := track.getLocal()
 
-		pi, ok := <-ch
+	for {
+		select {
+		case <-track.localCh:
+			local = track.getLocal()
+		case pi, ok := <-ch:
 			if !ok {
 				return
 			}
@@ -470,6 +470,7 @@ func writeLoop(conn *upConnection, track *upTrack, ch <-chan packetIndex) {
 			}
 		}
 	}
+}
 
 func rtcpUpListener(conn *upConnection, track *upTrack, r *webrtc.RTPReceiver) {
 	for {
@@ -637,7 +638,11 @@ func addDownConn(c *client, id string, remote *upConnection) (*downConnection, e
 	if c.down == nil {
 		c.down = make(map[string]*downConnection)
 	}
-	conn := &downConnection{id: id, pc: pc, remote: remote}
+	conn := &downConnection{
+		id:     id,
+		pc:     pc,
+		remote: remote,
+	}
 
 	c.mu.Lock()
 	defer c.mu.Unlock()

group.go

@@ -35,25 +35,39 @@ type upTrack struct {
 	lastSenderReport     uint32
 	lastSenderReportTime uint32
 
+	localCh    chan struct{} // signals that local has changed
+	writerDone chan struct{} // closed when the loop dies
+
 	mu    sync.Mutex
 	local []*downTrack
 }
 
+func (up *upTrack) notifyLocal() {
+	var s struct{}
+	select {
+	case up.localCh <- s:
+	case <-up.writerDone:
+	}
+}
+
 func (up *upTrack) addLocal(local *downTrack) {
 	up.mu.Lock()
-	defer up.mu.Unlock()
 	up.local = append(up.local, local)
+	up.mu.Unlock()
+	up.notifyLocal()
 }
 
 func (up *upTrack) delLocal(local *downTrack) bool {
 	up.mu.Lock()
-	defer up.mu.Unlock()
 	for i, l := range up.local {
 		if l == local {
 			up.local = append(up.local[:i], up.local[i+1:]...)
+			up.mu.Unlock()
+			up.notifyLocal()
 			return true
 		}
 	}
+	up.mu.Unlock()
 	return false
 }