Fix USB audio channels and remove redundant synchronization

USB audio configuration:
- Set playback to mono (microphone input from remote PC)
- Set capture to stereo (audio output to remote PC)
- Fixes audio input initialization failures and stereo output

Audio management optimizations:
- Remove redundant mutex in stopInputAudio (C layer provides synchronization)
- Remove unnecessary 100ms delay when switching audio sources
- Simplify error handling (Disconnect is idempotent)
- Remove time import (no longer needed)

audio.go

@@ -4,7 +4,6 @@ import (
 	"io"
 	"sync"
 	"sync/atomic"
-	"time"
 
 	"github.com/jetkvm/kvm/internal/audio"
 	"github.com/jetkvm/kvm/internal/logging"
@@ -49,7 +48,6 @@ func initAudio() {
 }
 
 func getAudioConfig() audio.AudioConfig {
-	// config is already loaded
 	cfg := audio.DefaultAudioConfig()
 	if config.AudioBitrate >= 64 && config.AudioBitrate <= 256 {
 		cfg.Bitrate = uint16(config.AudioBitrate)
@@ -160,9 +158,7 @@ func stopInputAudio() {
 		inRelay.Stop()
 	}
 	if inSource != nil {
-		inputSourceMutex.Lock()
 		(*inSource).Disconnect()
-		inputSourceMutex.Unlock()
 	}
 }
 
@@ -252,8 +248,6 @@ func SetAudioOutputSource(source string) error {
 	stopOutputAudio()
 	config.AudioOutputSource = source
 
-	time.Sleep(100 * time.Millisecond)
-
 	if err := startAudio(); err != nil {
 		audioLogger.Error().Err(err).Str("source", source).Msg("Failed to start audio output after source change")
 	}
@@ -328,10 +322,8 @@ func handleInputTrackForSession(track *webrtc.TrackRemote) {
 		}
 
 		if err := (*source).WriteMessage(0, opusData); err != nil {
-			if inputSource.Load() == source {
-				audioLogger.Warn().Err(err).Msg("failed to write audio message")
-				(*source).Disconnect()
-			}
+			audioLogger.Warn().Err(err).Msg("failed to write audio message")
+			(*source).Disconnect()
 		}
 
 		inputSourceMutex.Unlock()

internal/usbgadget/config.go

@@ -66,11 +66,11 @@ var defaultGadgetConfig = map[string]gadgetConfigItem{
 		path:       []string{"functions", "uac1.usb0"},
 		configPath: []string{"uac1.usb0"},
 		attrs: gadgetAttributes{
-			"p_chmask":         "3",     // Playback: stereo (2 channels)
+			"p_chmask":         "1",     // Playback: mono (1 channel for microphone)
 			"p_srate":          "48000", // Playback: 48kHz sample rate
 			"p_ssize":          "2",     // Playback: 16-bit (2 bytes)
 			"p_volume_present": "1",     // Playback: enable volume control
-			"c_chmask":         "1",     // Capture: mono (1 channel)
+			"c_chmask":         "3",     // Capture: stereo (2 channels for HDMI audio)
 			"c_srate":          "48000", // Capture: 48kHz sample rate
 			"c_ssize":          "2",     // Capture: 16-bit (2 bytes)
 			"c_volume_present": "0",     // Capture: no volume control