Fix race condition in setAudioTrack by using single critical section

Reduced mutex locking from 3 separate lock/unlock cycles to 1, eliminating
race window and improving performance. New relay is prepared within mutex,
then old resources are stopped and new relay started outside mutex to avoid
blocking during CGO calls.

audio.go

@@ -163,15 +163,32 @@ func setAudioTrack(audioTrack *webrtc.TrackLocalStaticSample) {
 	setAudioTrackMutex.Lock()
 	defer setAudioTrackMutex.Unlock()
 
+	// Capture old resources and update state in single critical section
 	audioMutex.Lock()
 	currentAudioTrack = audioTrack
 	oldRelay := outputRelay
 	oldSource := outputSource
 	outputRelay = nil
 	outputSource = nil
+
+	// Prepare new relay if needed
+	var newRelay *audio.OutputRelay
+	var newSource audio.AudioSource
+	if currentAudioTrack != nil && audioOutputEnabled.Load() {
+		ensureConfigLoaded()
+		alsaDevice := "hw:1,0"
+		if config.AudioOutputSource == "hdmi" {
+			alsaDevice = "hw:0,0"
+		}
+		newSource = audio.NewCgoOutputSource(alsaDevice)
+		newSource.SetConfig(getAudioConfig())
+		newRelay = audio.NewOutputRelay(newSource, currentAudioTrack)
+		outputSource = newSource
+		outputRelay = newRelay
+	}
 	audioMutex.Unlock()
 
-	// Stop relay and disconnect source outside mutex to avoid blocking during CGO calls
+	// Stop old resources outside mutex to avoid blocking during CGO calls
 	if oldRelay != nil {
 		oldRelay.Stop()
 	}
@@ -179,28 +196,9 @@ func setAudioTrack(audioTrack *webrtc.TrackLocalStaticSample) {
 		oldSource.Disconnect()
 	}
 
-	audioMutex.Lock()
-	if currentAudioTrack != nil && audioOutputEnabled.Load() {
-		ensureConfigLoaded()
-		alsaDevice := "hw:1,0"
-		if config.AudioOutputSource == "hdmi" {
-			alsaDevice = "hw:0,0"
-		}
-		newSource := audio.NewCgoOutputSource(alsaDevice)
-		newSource.SetConfig(getAudioConfig())
-		newRelay := audio.NewOutputRelay(newSource, currentAudioTrack)
-		outputSource = newSource
-		outputRelay = newRelay
-	}
-	audioMutex.Unlock()
-
-	// Capture relay reference and start it outside mutex
-	audioMutex.Lock()
-	relayToStart := outputRelay
-	audioMutex.Unlock()
-
-	if relayToStart != nil {
-		if err := relayToStart.Start(); err != nil {
+	// Start new relay outside mutex
+	if newRelay != nil {
+		if err := newRelay.Start(); err != nil {
 			audioLogger.Error().Err(err).Msg("Failed to start output relay")
 		}
 	}