From 7fe23c7bc5b480cadb24a4f3ec131ef3478ff423 Mon Sep 17 00:00:00 2001
From: Alex X <alexey.khit@gmail.com>
Date: Mon, 21 Apr 2025 20:09:04 +0300
Subject: [PATCH] Add wav backchannel (not used yet)

---
 pkg/wav/backchannel.go | 67 ++++++++++++++++++++++++++++++++++++++++++
 pkg/wav/wav.go         | 50 +++++++++++++++++++++++++++++++
 2 files changed, 117 insertions(+)
 create mode 100644 pkg/wav/backchannel.go
 create mode 100644 pkg/wav/wav.go

diff --git a/pkg/wav/backchannel.go b/pkg/wav/backchannel.go
new file mode 100644
index 00000000..f9697ee4
--- /dev/null
+++ b/pkg/wav/backchannel.go
@@ -0,0 +1,67 @@
+package wav
+
+import (
+	"github.com/AlexxIT/go2rtc/pkg/core"
+	"github.com/AlexxIT/go2rtc/pkg/shell"
+	"github.com/pion/rtp"
+)
+
+type Backchannel struct {
+	core.Connection
+	cmd *shell.Command
+}
+
+func NewBackchannel(cmd *shell.Command) (core.Producer, error) {
+	medias := []*core.Media{
+		{
+			Kind:      core.KindAudio,
+			Direction: core.DirectionSendonly,
+			Codecs: []*core.Codec{
+				//{Name: core.CodecPCML},
+				{Name: core.CodecPCMA},
+				{Name: core.CodecPCMU},
+			},
+		},
+	}
+
+	return &Backchannel{
+		Connection: core.Connection{
+			ID:         core.NewID(),
+			FormatName: "wav",
+			Protocol:   "pipe",
+			Medias:     medias,
+			Transport:  cmd,
+		},
+		cmd: cmd,
+	}, nil
+}
+
+func (c *Backchannel) GetTrack(media *core.Media, codec *core.Codec) (*core.Receiver, error) {
+	return nil, core.ErrCantGetTrack
+}
+
+func (c *Backchannel) AddTrack(media *core.Media, codec *core.Codec, track *core.Receiver) error {
+	wr, err := c.cmd.StdinPipe()
+	if err != nil {
+		return err
+	}
+
+	b := Header(track.Codec)
+	if _, err = wr.Write(b); err != nil {
+		return err
+	}
+
+	sender := core.NewSender(media, track.Codec)
+	sender.Handler = func(packet *rtp.Packet) {
+		if n, err := wr.Write(packet.Payload); err != nil {
+			c.Send += n
+		}
+	}
+	sender.HandleRTP(track)
+	c.Senders = append(c.Senders, sender)
+	return nil
+}
+
+func (c *Backchannel) Start() error {
+	return c.cmd.Run()
+}
diff --git a/pkg/wav/wav.go b/pkg/wav/wav.go
new file mode 100644
index 00000000..bf48fdf9
--- /dev/null
+++ b/pkg/wav/wav.go
@@ -0,0 +1,50 @@
+package wav
+
+import (
+	"encoding/binary"
+
+	"github.com/AlexxIT/go2rtc/pkg/core"
+)
+
+func Header(codec *core.Codec) []byte {
+	var fmt, size, extra byte
+
+	switch codec.Name {
+	case core.CodecPCML:
+		fmt = 1
+		size = 2
+	case core.CodecPCMA:
+		fmt = 6
+		size = 1
+		extra = 2
+	case core.CodecPCMU:
+		fmt = 7
+		size = 1
+		extra = 2
+	default:
+		return nil
+	}
+
+	channels := byte(codec.Channels)
+	if channels == 0 {
+		channels = 1
+	}
+
+	b := make([]byte, 0, 46) // cap with extra
+	b = append(b, "RIFF\xFF\xFF\xFF\xFFWAVEfmt "...)
+
+	b = append(b, 0x10+extra, 0, 0, 0)
+	b = append(b, fmt, 0)
+	b = append(b, channels, 0)
+	b = binary.LittleEndian.AppendUint32(b, codec.ClockRate)
+	b = binary.LittleEndian.AppendUint32(b, uint32(size*channels)*codec.ClockRate)
+	b = append(b, size*channels, 0)
+	b = append(b, size*8, 0)
+	if extra > 0 {
+		b = append(b, 0, 0) // ExtraParamSize (if PCM, then doesn't exist)
+	}
+
+	b = append(b, "data\xFF\xFF\xFF\xFF"...)
+
+	return b
+}