Add support resampling for PCM for WebRTC

pkg/pcm/pcm.go

@@ -0,0 +1,116 @@
+package pcm
+
+import (
+	"github.com/AlexxIT/go2rtc/pkg/core"
+	"github.com/pion/rtp"
+)
+
+func Resample(codec *core.Codec, sampleRate uint32, handler core.HandlerFunc) core.HandlerFunc {
+	n := float32(codec.ClockRate) / float32(sampleRate)
+
+	switch codec.Name {
+	case core.CodecPCMA:
+		return DownsampleByte(PCMAtoPCM, PCMtoPCMA, n, handler)
+	case core.CodecPCMU:
+		return DownsampleByte(PCMUtoPCM, PCMtoPCMU, n, handler)
+	case core.CodecPCM:
+		if n == 1 {
+			return ResamplePCM(PCMtoPCMA, handler)
+		}
+		return DownsamplePCM(PCMtoPCMA, n, handler)
+	}
+
+	panic(core.Caller())
+}
+
+func DownsampleByte(
+	toPCM func(byte) int16, fromPCM func(int16) byte, n float32, handler core.HandlerFunc,
+) core.HandlerFunc {
+	var sampleN, sampleSum float32
+	var ts uint32
+
+	return func(packet *rtp.Packet) {
+		samples := len(packet.Payload)
+		newLen := uint32((float32(samples) + sampleN) / n)
+
+		oldSamples := packet.Payload
+		newSamples := make([]byte, newLen)
+
+		var i int
+		for _, sample := range oldSamples {
+			sampleSum += float32(toPCM(sample))
+			if sampleN++; sampleN >= n {
+				newSamples[i] = fromPCM(int16(sampleSum / n))
+				i++
+
+				sampleSum = 0
+				sampleN -= n
+			}
+		}
+
+		ts += newLen
+
+		clone := *packet
+		clone.Payload = newSamples
+		clone.Timestamp = ts
+		handler(&clone)
+	}
+}
+
+func ResamplePCM(fromPCM func(int16) byte, handler core.HandlerFunc) core.HandlerFunc {
+	var ts uint32
+
+	return func(packet *rtp.Packet) {
+		len1 := len(packet.Payload)
+		len2 := len1 / 2
+
+		oldSamples := packet.Payload
+		newSamples := make([]byte, len2)
+
+		var i2 int
+		for i1 := 0; i1 < len1; i1 += 2 {
+			sample := int16(uint16(oldSamples[i1])<<8 | uint16(oldSamples[i1+1]))
+			newSamples[i2] = fromPCM(sample)
+			i2++
+		}
+
+		ts += uint32(len2)
+
+		clone := *packet
+		clone.Payload = newSamples
+		clone.Timestamp = ts
+		handler(&clone)
+	}
+}
+
+func DownsamplePCM(fromPCM func(int16) byte, n float32, handler core.HandlerFunc) core.HandlerFunc {
+	var sampleN, sampleSum float32
+	var ts uint32
+
+	return func(packet *rtp.Packet) {
+		samples := len(packet.Payload) / 2
+		newLen := uint32((float32(samples) + sampleN) / n)
+
+		oldSamples := packet.Payload
+		newSamples := make([]byte, newLen)
+
+		var i2 int
+		for i1 := 0; i1 < len(packet.Payload); i1 += 2 {
+			sampleSum += float32(int16(uint16(oldSamples[i1])<<8 | uint16(oldSamples[i1+1])))
+			if sampleN++; sampleN >= n {
+				newSamples[i2] = fromPCM(int16(sampleSum / n))
+				i2++
+
+				sampleSum = 0
+				sampleN -= n
+			}
+		}
+
+		ts += newLen
+
+		clone := *packet
+		clone.Payload = newSamples
+		clone.Timestamp = ts
+		handler(&clone)
+	}
+}

pkg/webrtc/consumer.go

@@ -5,11 +5,12 @@ import (
 	"github.com/AlexxIT/go2rtc/pkg/core"
 	"github.com/AlexxIT/go2rtc/pkg/h264"
 	"github.com/AlexxIT/go2rtc/pkg/h265"
+	"github.com/AlexxIT/go2rtc/pkg/pcm"
 	"github.com/pion/rtp"
 )
 
 func (c *Conn) GetMedias() []*core.Media {
-	return c.medias
+	return WithResampling(c.medias)
 }
 
 func (c *Conn) AddTrack(media *core.Media, codec *core.Codec, track *core.Receiver) error {
@@ -31,15 +32,16 @@ func (c *Conn) AddTrack(media *core.Media, codec *core.Codec, track *core.Receiv
 	}
 
 	localTrack := c.getTranseiver(media.ID).Sender().Track().(*Track)
+	payloadType := codec.PayloadType
 
-	sender := core.NewSender(media, track.Codec)
+	sender := core.NewSender(media, codec)
 	sender.Handler = func(packet *rtp.Packet) {
 		c.send += packet.MarshalSize()
 		//important to send with remote PayloadType
-		_ = localTrack.WriteRTP(codec.PayloadType, packet)
+		_ = localTrack.WriteRTP(payloadType, packet)
 	}
 
-	switch codec.Name {
+	switch track.Codec.Name {
 	case core.CodecH264:
 		sender.Handler = h264.RTPPay(1200, sender.Handler)
 		if track.Codec.IsRTP() {
@@ -55,6 +57,15 @@ func (c *Conn) AddTrack(media *core.Media, codec *core.Codec, track *core.Receiv
 		if track.Codec.IsRTP() {
 			sender.Handler = h265.RTPDepay(track.Codec, sender.Handler)
 		}
+
+	case core.CodecPCMA, core.CodecPCMU, core.CodecPCM:
+		if codec.ClockRate == 0 {
+			if codec.Name == core.CodecPCM {
+				codec.Name = core.CodecPCMA
+			}
+			codec.ClockRate = 8000
+			sender.Handler = pcm.Resample(track.Codec, 8000, sender.Handler)
+		}
 	}
 
 	sender.HandleRTP(track)

pkg/webrtc/helpers.go

@@ -52,6 +52,53 @@ func UnmarshalMedias(descriptions []*sdp.MediaDescription) (medias []*core.Media
 	return
 }
 
+func WithResampling(medias []*core.Media) []*core.Media {
+	for _, media := range medias {
+		if media.Kind != core.KindAudio || media.Direction != core.DirectionSendonly {
+			continue
+		}
+
+		var pcma, pcmu, pcm *core.Codec
+
+		for _, codec := range media.Codecs {
+			switch codec.Name {
+			case core.CodecPCMA:
+				if codec.ClockRate != 0 {
+					pcma = codec
+				} else {
+					pcma = nil
+				}
+			case core.CodecPCMU:
+				if codec.ClockRate != 0 {
+					pcmu = codec
+				} else {
+					pcmu = nil
+				}
+			case core.CodecPCM:
+				pcm = codec
+			}
+		}
+
+		if pcma != nil {
+			pcma = pcma.Clone()
+			pcma.ClockRate = 0 // reset clock rate so will match any
+			media.Codecs = append(media.Codecs, pcma)
+		}
+		if pcmu != nil {
+			pcmu = pcmu.Clone()
+			pcmu.ClockRate = 0
+			media.Codecs = append(media.Codecs, pcmu)
+		}
+		if pcma != nil && pcm == nil {
+			pcm = pcma.Clone()
+			pcm.Name = core.CodecPCM
+			media.Codecs = append(media.Codecs, pcm)
+		}
+	}
+
+	return medias
+}
+
 func NewCandidate(network, address string) (string, error) {
 	i := strings.LastIndexByte(address, ':')
 	if i < 0 {