feat: support setting advanced ALSA configuration

README.md

@@ -137,6 +137,8 @@ device_type: computer # Spotify device type (icon)
 audio_device: default # ALSA audio device to use for playback
 mixer_device: '' # ALSA mixer device for volume synchronization 
 mixer_control_name: Master # ALSA mixer control name for volume synchronization
+audio_buffer_time: 500000 # Audio buffer time in microseconds, ALSA only
+audio_period_count: 4 # Number of periods to request, ALSA only
 bitrate: 160 # Playback bitrate (96, 160, 320)
 volume_steps: 100 # Volume steps count
 initial_volume: 100 # Initial volume in steps (not applied to the mixer device)

cmd/daemon/main.go

@@ -133,8 +133,10 @@ func (app *App) newAppPlayer(ctx context.Context, creds any) (_ *AppPlayer, err
 	if appPlayer.player, err = player.NewPlayer(
 		appPlayer.sess.Spclient(), appPlayer.sess.AudioKey(),
 		!app.cfg.NormalisationDisabled, app.cfg.NormalisationPregain,
-		appPlayer.countryCode, app.cfg.AudioBackend, app.cfg.AudioDevice, app.cfg.MixerDevice, app.cfg.MixerControlName,
-		app.cfg.VolumeSteps, app.cfg.ExternalVolume, appPlayer.volumeUpdate,
+		appPlayer.countryCode,
+		app.cfg.AudioBackend, app.cfg.AudioDevice, app.cfg.MixerDevice, app.cfg.MixerControlName,
+		app.cfg.AudioBufferTime, app.cfg.AudioPeriodCount,
+		app.cfg.ExternalVolume, appPlayer.volumeUpdate,
 	); err != nil {
 		return nil, fmt.Errorf("failed initializing player: %w", err)
 	}
@@ -348,6 +350,8 @@ type Config struct {
 	AudioDevice           string    `koanf:"audio_device"`
 	MixerDevice           string    `koanf:"mixer_device"`
 	MixerControlName      string    `koanf:"mixer_control_name"`
+	AudioBufferTime       int       `koanf:"audio_buffer_time"`
+	AudioPeriodCount      int       `koanf:"audio_period_count"`
 	Bitrate               int       `koanf:"bitrate"`
 	VolumeSteps           uint32    `koanf:"volume_steps"`
 	InitialVolume         uint32    `koanf:"initial_volume"`

config_schema.json

@@ -84,6 +84,16 @@
           "description": "Which control should be used, leave empty for default. Only useful in combination with 'mixer_device'",
           "default": "Master"
         },
+        "audio_buffer_time": {
+          "type": "integer",
+          "description": "The audio buffer time in microseconds. Available for ALSA backend only, leave empty for default",
+          "default": 0
+        },
+        "audio_period_count": {
+          "type": "integer",
+          "description": "The number of audio periods to request. Available for ALSA backend only, leave empty for default",
+          "default": 0
+        },
         "server": {
           "type": "object",
           "properties": {

output/driver-alsa.go

@@ -20,8 +20,8 @@ import (
 )
 
 const (
-	BufferTimeMicro = 500_000
-	NumPeriods      = 4 // number of periods requested
+	defaultBufferTimeMicro = 500_000
+	defaultNumPeriods      = 4
 )
 
 type alsaOutput struct {
@@ -32,9 +32,11 @@ type alsaOutput struct {
 
 	lock sync.Mutex
 
-	pcmHandle  *C.snd_pcm_t // nil when pcmHandle is closed
-	periodSize int
-	bufferSize int
+	pcmHandle   *C.snd_pcm_t // nil when pcmHandle is closed
+	bufferTime  int
+	periodCount int
+	periodSize  int
+	bufferSize  int
 
 	externalVolume bool
 
@@ -68,6 +70,18 @@ func newAlsaOutput(opts *NewOutputOptions) (*alsaOutput, error) {
 		volumeUpdate:   opts.VolumeUpdate,
 	}
 
+	if opts.BufferTimeMicro == 0 {
+		out.bufferTime = defaultBufferTimeMicro
+	} else {
+		out.bufferTime = opts.BufferTimeMicro
+	}
+
+	if opts.PeriodCount == 0 {
+		out.periodCount = defaultNumPeriods
+	} else {
+		out.periodCount = opts.PeriodCount
+	}
+
 	if err := out.setupMixer(); err != nil {
 		if uintptr(unsafe.Pointer(out.mixerHandle)) != 0 {
 			C.snd_mixer_close(out.mixerHandle)
@@ -120,7 +134,7 @@ func (out *alsaOutput) setupPcm() error {
 		return out.alsaError("snd_pcm_hw_params_set_rate_near", err)
 	}
 
-	bufferTime := C.uint(BufferTimeMicro)
+	bufferTime := C.uint(out.bufferTime)
 	if err := C.snd_pcm_hw_params_set_buffer_time_near(out.pcmHandle, hwparams, &bufferTime, nil); err < 0 {
 		return out.alsaError("snd_pcm_hw_params_set_buffer_time_near", err)
 	}
@@ -132,7 +146,7 @@ func (out *alsaOutput) setupPcm() error {
 	if err := C.snd_pcm_hw_params_get_buffer_size(hwparams, &bufferSize); err < 0 {
 		return out.alsaError("snd_pcm_hw_params_get_buffer_size", err)
 	}
-	var periodSize C.snd_pcm_uframes_t = C.snd_pcm_uframes_t(bufferSize) / NumPeriods
+	var periodSize C.snd_pcm_uframes_t = C.snd_pcm_uframes_t(bufferSize) / C.snd_pcm_uframes_t(out.periodCount)
 	if err := C.snd_pcm_hw_params_set_period_size_near(out.pcmHandle, hwparams, &periodSize, nil); err < 0 {
 		return out.alsaError("snd_pcm_hw_params_set_period_size_near", err)
 	}

output/output.go

@@ -67,6 +67,16 @@ type NewOutputOptions struct {
 	// This only works in combination with Mixer
 	Control string
 
+	// BufferTimeMicro is the buffer time in microseconds.
+	//
+	// This is only supported on the alsa backend.
+	BufferTimeMicro int
+
+	// PeriodCount is the number of periods to request.
+	//
+	// This is only supported on the alsa backend.
+	PeriodCount int
+
 	// InitialVolume specifies the initial output volume.
 	//
 	// This is only supported on the alsa backend. The PulseAudio backend uses

player/player.go

@@ -65,7 +65,15 @@ type playerCmdDataSet struct {
 	drop    bool
 }
 
-func NewPlayer(sp *spclient.Spclient, audioKey *audio.KeyProvider, normalisationEnabled bool, normalisationPregain float32, countryCode *string, backend, device, mixer string, control string, volumeSteps uint32, externalVolume bool, volumeUpdate chan float32) (*Player, error) {
+// FIXME: we should probably use a struct here
+func NewPlayer(
+	sp *spclient.Spclient, audioKey *audio.KeyProvider,
+	normalisationEnabled bool, normalisationPregain float32,
+	countryCode *string,
+	backend, device, mixer, control string,
+	bufferTime, periodCount int,
+	externalVolume bool, volumeUpdate chan float32,
+) (*Player, error) {
 	p := &Player{
 		sp:                   sp,
 		audioKey:             audioKey,
@@ -74,16 +82,18 @@ func NewPlayer(sp *spclient.Spclient, audioKey *audio.KeyProvider, normalisation
 		countryCode:          countryCode,
 		newOutput: func(reader librespot.Float32Reader, volume float32) (output.Output, error) {
 			return output.NewOutput(&output.NewOutputOptions{
-				Backend:        backend,
-				Reader:         reader,
-				SampleRate:     SampleRate,
-				ChannelCount:   Channels,
-				Device:         device,
-				Mixer:          mixer,
-				Control:        control,
-				InitialVolume:  volume,
-				ExternalVolume: externalVolume,
-				VolumeUpdate:   volumeUpdate,
+				Backend:         backend,
+				Reader:          reader,
+				SampleRate:      SampleRate,
+				ChannelCount:    Channels,
+				Device:          device,
+				Mixer:           mixer,
+				Control:         control,
+				InitialVolume:   volume,
+				BufferTimeMicro: bufferTime,
+				PeriodCount:     periodCount,
+				ExternalVolume:  externalVolume,
+				VolumeUpdate:    volumeUpdate,
 			})
 		},