fix: wait for audio relay goroutine to exit before disconnecting source

audio.go

@@ -22,7 +22,7 @@ var (
 	audioLogger          zerolog.Logger
 	currentAudioTrack    *webrtc.TrackLocalStaticSample
 	inputTrackHandling   atomic.Bool
-	useUSBForAudioOutput bool
+	useUSBForAudioOutput atomic.Bool
 	audioOutputEnabled   atomic.Bool
 	audioInputEnabled    atomic.Bool
 )
@@ -32,7 +32,7 @@ func initAudio() {
 
 	// Load audio output source from config
 	ensureConfigLoaded()
-	useUSBForAudioOutput = config.AudioOutputSource == "usb"
+	useUSBForAudioOutput.Store(config.AudioOutputSource == "usb")
 
 	// Enable both by default
 	audioOutputEnabled.Store(true)
@@ -57,7 +57,7 @@ func startAudio() error {
 	// Start output audio if not running and enabled
 	if outputSource == nil && audioOutputEnabled.Load() {
 		alsaDevice := "hw:0,0" // HDMI
-		if useUSBForAudioOutput {
+		if useUSBForAudioOutput.Load() {
 			alsaDevice = "hw:1,0" // USB
 		}
 
@@ -167,16 +167,17 @@ func SetAudioOutputSource(useUSB bool) error {
 	audioMutex.Lock()
 	defer audioMutex.Unlock()
 
-	if useUSBForAudioOutput == useUSB {
+	if useUSBForAudioOutput.Load() == useUSB {
 		return nil
 	}
 
 	audioLogger.Info().
-		Bool("old_usb", useUSBForAudioOutput).
+		Bool("old_usb", useUSBForAudioOutput.Load()).
 		Bool("new_usb", useUSB).
 		Msg("Switching audio output source")
 
-	useUSBForAudioOutput = useUSB
+	oldValue := useUSBForAudioOutput.Load()
+	useUSBForAudioOutput.Store(useUSB)
 
 	ensureConfigLoaded()
 	if useUSB {
@@ -186,6 +187,7 @@ func SetAudioOutputSource(useUSB bool) error {
 	}
 	if err := SaveConfig(); err != nil {
 		audioLogger.Error().Err(err).Msg("Failed to save config")
+		useUSBForAudioOutput.Store(oldValue)
 		return err
 	}
 

internal/audio/relay.go

@@ -20,7 +20,8 @@ type OutputRelay struct {
 	cancel     context.CancelFunc
 	logger     zerolog.Logger
 	running    atomic.Bool
-	sample     media.Sample // Reusable sample for zero-allocation hot path
+	sample     media.Sample
+	stopped    chan struct{}
 
 	// Stats (Uint32: overflows after 2.7 years @ 50fps, faster atomics on 32-bit ARM)
 	framesRelayed atomic.Uint32
@@ -38,8 +39,9 @@ func NewOutputRelay(source AudioSource, audioTrack *webrtc.TrackLocalStaticSampl
 		ctx:        ctx,
 		cancel:     cancel,
 		logger:     logger,
+		stopped:    make(chan struct{}),
 		sample: media.Sample{
-			Duration: 20 * time.Millisecond, // Constant for all Opus frames
+			Duration: 20 * time.Millisecond,
 		},
 	}
 }
@@ -55,13 +57,15 @@ func (r *OutputRelay) Start() error {
 	return nil
 }
 
-// Stop stops the relay
+// Stop stops the relay and waits for goroutine to exit
 func (r *OutputRelay) Stop() {
 	if !r.running.Swap(false) {
 		return
 	}
 
 	r.cancel()
+	<-r.stopped
+
 	r.logger.Debug().
 		Uint32("frames_relayed", r.framesRelayed.Load()).
 		Uint32("frames_dropped", r.framesDropped.Load()).
@@ -70,6 +74,8 @@ func (r *OutputRelay) Stop() {
 
 // relayLoop continuously reads from audio source and writes to WebRTC
 func (r *OutputRelay) relayLoop() {
+	defer close(r.stopped)
+
 	const reconnectDelay = 1 * time.Second
 
 	for r.running.Load() {

jsonrpc.go

@@ -899,7 +899,7 @@ func updateUsbRelatedConfig(wasAudioEnabled bool) error {
 	if config.UsbDevices != nil && !config.UsbDevices.Audio && config.AudioOutputSource == "usb" {
 		audioMutex.Lock()
 		config.AudioOutputSource = "hdmi"
-		useUSBForAudioOutput = false
+		useUSBForAudioOutput.Store(false)
 		audioSourceChanged = true
 		audioMutex.Unlock()
 	}
@@ -908,7 +908,7 @@ func updateUsbRelatedConfig(wasAudioEnabled bool) error {
 	if config.UsbDevices != nil && config.UsbDevices.Audio && !wasAudioEnabled {
 		audioMutex.Lock()
 		config.AudioOutputSource = "usb"
-		useUSBForAudioOutput = true
+		useUSBForAudioOutput.Store(true)
 		audioSourceChanged = true
 		audioMutex.Unlock()
 	}
@@ -970,8 +970,10 @@ func rpcSetUsbDeviceState(device string, enabled bool) error {
 }
 
 func rpcGetAudioOutputSource() (string, error) {
-	ensureConfigLoaded()
-	return config.AudioOutputSource, nil
+	if useUSBForAudioOutput.Load() {
+		return "usb", nil
+	}
+	return "hdmi", nil
 }
 
 func rpcSetAudioOutputSource(source string) error {