Add wav backchannel (not used yet)

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
+}