Add supported codec check for alsa source

internal/alsa/alsa_linux.go

@@ -44,7 +44,7 @@ func apiAlsa(w http.ResponseWriter, r *http.Request) {
 		info, err := dev.Info()
 		if err == nil {
 			formats := formatsToString(dev.ListFormats())
-			r1, r2 := dev.RangeSampleRates()
+			r1, r2 := dev.RangeRates()
 			c1, c2 := dev.RangeChannels()
 			source := &api.Source{
 				Name: info.ID + " / " + info.Name + " / " + info.SubName,

pkg/alsa/capture_linux.go

@@ -3,6 +3,7 @@ package alsa
 import (
 	"github.com/AlexxIT/go2rtc/pkg/alsa/device"
 	"github.com/AlexxIT/go2rtc/pkg/core"
+	"github.com/AlexxIT/go2rtc/pkg/pcm"
 	"github.com/pion/rtp"
 )
 
@@ -33,19 +34,25 @@ func newCapture(dev *device.Device) (*Capture, error) {
 	}, nil
 }
 
-// readBufferSize - 20ms * 2 bytes per sample * 16000 frames per second * 2 channels / 1000ms per second
-const readBufferSize = 20 * 2 * 16000 * 2 / 1000
-
-// bytesPerFrame - 2 bytes per sample * 2 channels
-const bytesPerFrame = 2 * 2
-
 func (c *Capture) Start() error {
-	if err := c.dev.SetHWParams(device.SNDRV_PCM_FORMAT_S16_LE, 16000, 2); err != nil {
+	dst := c.Medias[0].Codecs[0]
+	src := &core.Codec{
+		Name:      dst.Name,
+		ClockRate: c.dev.GetRateNear(dst.ClockRate),
+		Channels:  c.dev.GetChannelsNear(dst.Channels),
+	}
+
+	if err := c.dev.SetHWParams(device.SNDRV_PCM_FORMAT_S16_LE, src.ClockRate, src.Channels); err != nil {
 		return err
 	}
 
+	transcode := transcodeFunc(dst, src)
+	frameBytes := int(pcm.BytesPerFrame(src))
+
 	var ts uint32
 
+	// readBufferSize for 20ms interval
+	readBufferSize := 20 * frameBytes * int(src.ClockRate) / 1000
 	b := make([]byte, readBufferSize)
 	for {
 		n, err := c.dev.Read(b)
@@ -65,25 +72,19 @@ func (c *Capture) Start() error {
 				Marker:    true,
 				Timestamp: ts,
 			},
-			Payload: stereoToMono(b[:n]),
+			Payload: transcode(b[:n]),
 		}
 		c.Receivers[0].WriteRTP(pkt)
 
-		ts += uint32(n / bytesPerFrame)
+		ts += uint32(n / frameBytes)
 	}
 }
 
-func stereoToMono(stereo []byte) (mono []byte) {
+func transcodeFunc(dst, src *core.Codec) func([]byte) []byte {
-	n := len(stereo)
+	if dst.ClockRate == src.ClockRate && dst.Channels == src.Channels {
-	mono = make([]byte, n/2)
+		return func(b []byte) []byte {
-	var i, j int
+			return b
-	for i < n {
+		}
-		mono[j] = stereo[i]
-		j++
-		i++
-		mono[j] = stereo[i]
-		j++
-		i += 3
 	}
-	return
+	return pcm.Transcode(dst, src)
 }

pkg/alsa/device/device_linux.go

@@ -75,29 +75,55 @@ func (d *Device) Info() (*Info, error) {
 	}, nil
 }
 
+func (d *Device) CheckFormat(format byte) bool {
+	return d.checkMask(SNDRV_PCM_HW_PARAM_FORMAT, uint32(format))
+}
+
 func (d *Device) ListFormats() (formats []byte) {
 	for i := byte(0); i <= 28; i++ {
-		if d.checkMask(SNDRV_PCM_HW_PARAM_FORMAT, uint32(i)) {
+		if d.CheckFormat(i) {
 			formats = append(formats, i)
 		}
 	}
 	return
 }
 
+func (d *Device) RangeRates() (uint32, uint32) {
+	return d.getInterval(SNDRV_PCM_HW_PARAM_RATE)
+}
+
 func (d *Device) RangeChannels() (byte, byte) {
 	minCh, maxCh := d.getInterval(SNDRV_PCM_HW_PARAM_CHANNELS)
 	return byte(minCh), byte(maxCh)
 }
 
-func (d *Device) RangeSampleRates() (uint32, uint32) {
+func (d *Device) GetRateNear(rate uint32) uint32 {
-	return d.getInterval(SNDRV_PCM_HW_PARAM_RATE)
+	r1, r2 := d.RangeRates()
+	if rate < r1 {
+		return r1
+	}
+	if rate > r2 {
+		return r2
+	}
+	return rate
+}
+
+func (d *Device) GetChannelsNear(channels byte) byte {
+	c1, c2 := d.RangeChannels()
+	if channels < c1 {
+		return c1
+	}
+	if channels > c2 {
+		return c2
+	}
+	return channels
 }
 
 const bufferSize = 4096
 
-func (d *Device) SetHWParams(format byte, sampleRate uint32, channels byte) error {
+func (d *Device) SetHWParams(format byte, rate uint32, channels byte) error {
 	d.setInterval(SNDRV_PCM_HW_PARAM_CHANNELS, uint32(channels))
-	d.setInterval(SNDRV_PCM_HW_PARAM_RATE, sampleRate)
+	d.setInterval(SNDRV_PCM_HW_PARAM_RATE, rate)
 	d.setMask(SNDRV_PCM_HW_PARAM_FORMAT, uint32(format))
 	//d.setMask(SNDRV_PCM_HW_PARAM_SUBFORMAT, 0)
 

pkg/alsa/open_linux.go

@@ -1,6 +1,7 @@
 package alsa
 
 import (
+	"errors"
 	"fmt"
 	"net/url"
 
@@ -26,6 +27,11 @@ func Open(rawURL string) (core.Producer, error) {
 		return nil, err
 	}
 
+	if !dev.CheckFormat(device.SNDRV_PCM_FORMAT_S16_LE) {
+		_ = dev.Close()
+		return nil, errors.New("alsa: format S16LE not supported")
+	}
+
 	switch path[len(path)-1] {
 	case 'p': // playback
 		return newPlayback(dev)
@@ -34,6 +40,5 @@ func Open(rawURL string) (core.Producer, error) {
 	}
 
 	_ = dev.Close()
-
 	return nil, fmt.Errorf("alsa: unknown path: %s", path)
 }

pkg/alsa/playback_linux.go

@@ -43,20 +43,10 @@ func (p *Playback) GetTrack(media *core.Media, codec *core.Codec) (*core.Receive
 
 func (p *Playback) AddTrack(media *core.Media, codec *core.Codec, track *core.Receiver) error {
 	src := track.Codec
-
-	// support probe
-	if src.Name == core.CodecAny {
-		src = &core.Codec{
-			Name:      core.CodecPCML,
-			ClockRate: 16000,
-			Channels:  2,
-		}
-	}
-
 	dst := &core.Codec{
 		Name:      core.CodecPCML,
-		ClockRate: src.ClockRate,
+		ClockRate: p.dev.GetRateNear(src.ClockRate),
-		Channels:  2,
+		Channels:  p.dev.GetChannelsNear(src.Channels),
 	}
 	sender := core.NewSender(media, dst)
 
@@ -74,7 +64,7 @@ func (p *Playback) AddTrack(media *core.Media, codec *core.Codec, track *core.Re
 	// - Formats: S16_LE, S32_LE
 	// - ClockRates: 8000 - 192000
 	// - Channels: 2 - 10
-	err := p.dev.SetHWParams(device.SNDRV_PCM_FORMAT_S16_LE, dst.ClockRate, 2)
+	err := p.dev.SetHWParams(device.SNDRV_PCM_FORMAT_S16_LE, dst.ClockRate, byte(dst.Channels))
 	if err != nil {
 		return err
 	}