Fix USB Audio Gadget sample rate constraints

USB Audio Gadget (hw:1,0) hardware only supports 48kHz for both capture
and playback due to configfs p_srate/c_srate being hardcoded. This commit
ensures both audio paths respect this hardware limitation:

- Output path: Force 48kHz when using hw:1,0, allow configurable rates for HDMI
- Input path: Always use 48kHz regardless of UI configuration
- Calculate frame size dynamically based on actual sample rate used

Also removes redundant comments that don't add debugging or maintainability value.

audio.go

@@ -49,28 +49,24 @@ func initAudio() {
 func getAudioConfig() audio.AudioConfig {
 	cfg := audio.DefaultAudioConfig()
 
-	// Apply bitrate (64-256 kbps)
 	if config.AudioBitrate >= 64 && config.AudioBitrate <= 256 {
 		cfg.Bitrate = uint16(config.AudioBitrate)
 	} else if config.AudioBitrate != 0 {
 		audioLogger.Warn().Int("bitrate", config.AudioBitrate).Msg("Invalid audio bitrate, using default")
 	}
 
-	// Apply complexity (0-10)
 	if config.AudioComplexity >= 0 && config.AudioComplexity <= 10 {
 		cfg.Complexity = uint8(config.AudioComplexity)
 	} else if config.AudioComplexity != 0 {
 		audioLogger.Warn().Int("complexity", config.AudioComplexity).Msg("Invalid audio complexity, using default")
 	}
 
-	// Apply buffer periods (2-24)
 	if config.AudioBufferPeriods >= 2 && config.AudioBufferPeriods <= 24 {
 		cfg.BufferPeriods = uint8(config.AudioBufferPeriods)
 	} else if config.AudioBufferPeriods != 0 {
 		audioLogger.Warn().Int("buffer_periods", config.AudioBufferPeriods).Msg("Invalid buffer periods, using default")
 	}
 
-	// Apply sample rate (Opus supports: 8k, 12k, 16k, 24k, 48k)
 	switch config.AudioSampleRate {
 	case 8000, 12000, 16000, 24000, 48000:
 		cfg.SampleRate = uint32(config.AudioSampleRate)
@@ -80,7 +76,6 @@ func getAudioConfig() audio.AudioConfig {
 		}
 	}
 
-	// Apply packet loss percentage (0-100)
 	if config.AudioPacketLossPerc >= 0 && config.AudioPacketLossPerc <= 100 {
 		cfg.PacketLossPerc = uint8(config.AudioPacketLossPerc)
 	} else if config.AudioPacketLossPerc != 0 {
@@ -118,7 +113,6 @@ func startAudio() error {
 		inputErr = startInputAudioUnderMutex(getAlsaDevice("usb"))
 	}
 
-	// Simplified error handling - both errors are worth reporting
 	if outputErr != nil || inputErr != nil {
 		if outputErr != nil && inputErr != nil {
 			return fmt.Errorf("audio start failed - output: %w, input: %v", outputErr, inputErr)

internal/audio/cgo_source.go

@@ -83,7 +83,13 @@ func (c *CgoSource) Connect() error {
 func (c *CgoSource) connectOutput() error {
 	os.Setenv("ALSA_CAPTURE_DEVICE", c.alsaDevice)
 
-	frameSize := uint16(c.config.SampleRate * 20 / 1000)
+	// USB Audio Gadget (hw:1,0) only supports 48kHz
+	// For HDMI (hw:0,0), use configured sample rate
+	sampleRate := c.config.SampleRate
+	if c.alsaDevice == "hw:1,0" {
+		sampleRate = 48000
+	}
+	frameSize := uint16(sampleRate * 20 / 1000)
 
 	c.logger.Debug().
 		Uint16("bitrate_kbps", c.config.Bitrate).
@@ -91,7 +97,7 @@ func (c *CgoSource) connectOutput() error {
 		Bool("dtx", c.config.DTXEnabled).
 		Bool("fec", c.config.FECEnabled).
 		Uint8("buffer_periods", c.config.BufferPeriods).
-		Uint32("sample_rate", c.config.SampleRate).
+		Uint32("sample_rate", sampleRate).
 		Uint16("frame_size", frameSize).
 		Uint8("packet_loss_perc", c.config.PacketLossPerc).
 		Msg("Initializing audio capture")
@@ -99,7 +105,7 @@ func (c *CgoSource) connectOutput() error {
 	C.update_audio_constants(
 		C.uint(uint32(c.config.Bitrate)*1000),
 		C.uchar(c.config.Complexity),
-		C.uint(c.config.SampleRate),
+		C.uint(sampleRate),
 		C.uchar(2),
 		C.ushort(frameSize),
 		C.ushort(1500),
@@ -125,10 +131,13 @@ func (c *CgoSource) connectOutput() error {
 func (c *CgoSource) connectInput() error {
 	os.Setenv("ALSA_PLAYBACK_DEVICE", c.alsaDevice)
 
-	frameSize := uint16(c.config.SampleRate * 20 / 1000)
+	// USB Audio Gadget (hw:1,0) is hardcoded to 48kHz in usbgadget/config.go
+	// Always use 48kHz for input path regardless of UI configuration
+	const inputSampleRate = 48000
+	frameSize := uint16(inputSampleRate * 20 / 1000)
 
 	C.update_audio_decoder_constants(
-		C.uint(c.config.SampleRate),
+		C.uint(inputSampleRate),
 		C.uchar(1),
 		C.ushort(frameSize),
 		C.ushort(1500),

ui/src/routes/devices.$id.settings.audio.tsx

@@ -20,18 +20,15 @@ interface AudioConfigResult {
   packet_loss_perc: number;
 }
 
-// UI display defaults - used to mark default options in dropdown menus
-// Note: These should match backend defaults in config.go, but are fetched dynamically from API
 const AUDIO_DEFAULTS = {
   bitrate: 192,
   complexity: 8,
-  packetLossPerc: 20,  // Backend default is 20, not 0
+  packetLossPerc: 20,
 } as const;
 
 export default function SettingsAudioRoute() {
   const { send } = useJsonRpc();
 
-  // Helper function to handle RPC errors consistently
   const handleRpcError = (resp: JsonRpcResponse, defaultMsg?: string) => {
     if ("error" in resp) {
       notifications.error(String(resp.error.data || defaultMsg || m.unknown_error()));
@@ -64,7 +61,6 @@ export default function SettingsAudioRoute() {
   } = useSettingsStore();
 
   useEffect(() => {
-    // Load boolean settings
     send("getAudioOutputEnabled", {}, (resp: JsonRpcResponse) => {
       if ("error" in resp) return;
       setAudioOutputEnabled(resp.result as boolean);
@@ -80,7 +76,6 @@ export default function SettingsAudioRoute() {
       setAudioOutputSource(resp.result as string);
     });
 
-    // Load complex audio configuration
     send("getAudioConfig", {}, (resp: JsonRpcResponse) => {
       if ("error" in resp) return;
       const config = resp.result as AudioConfigResult;
@@ -137,7 +132,6 @@ export default function SettingsAudioRoute() {
     });
   };
 
-  // Create a configuration object from current state
   const getCurrentConfig = () => ({
     bitrate: audioBitrate,
     complexity: audioComplexity,