From bf248c49c38493fba50a72a7c7f683615e1b8fa4 Mon Sep 17 00:00:00 2001
From: Alexey Khit <alexey.khit@gmail.com>
Date: Mon, 21 Aug 2023 15:34:53 +0300
Subject: [PATCH] Add support two channel PCM family audio #580

---
 pkg/mp4/consumer.go |  7 ++++++-
 pkg/pcm/flac.go     | 12 ++++--------
 pkg/pcm/pcm.go      |  4 ++++
 3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/pkg/mp4/consumer.go b/pkg/mp4/consumer.go
index 89c73cf7..8d0beef9 100644
--- a/pkg/mp4/consumer.go
+++ b/pkg/mp4/consumer.go
@@ -130,8 +130,13 @@ func (c *Consumer) AddTrack(media *core.Media, _ *core.Codec, track *core.Receiv
 			}
 		case core.CodecOpus, core.CodecMP3: // no changes
 		case core.CodecPCMA, core.CodecPCMU, core.CodecPCM, core.CodecPCML:
-			handler.Handler = pcm.FLACEncoder(track.Codec, handler.Handler)
 			codec.Name = core.CodecFLAC
+			if codec.Channels == 2 {
+				// hacky way for support two channels audio
+				codec.Channels = 1
+				codec.ClockRate *= 2
+			}
+			handler.Handler = pcm.FLACEncoder(track.Codec.Name, codec.ClockRate, handler.Handler)
 
 		default:
 			handler.Handler = nil
diff --git a/pkg/pcm/flac.go b/pkg/pcm/flac.go
index fdbe5190..808d4a75 100644
--- a/pkg/pcm/flac.go
+++ b/pkg/pcm/flac.go
@@ -48,13 +48,9 @@ func FLACHeader(magic bool, sampleRate uint32) []byte {
 var table8 *crc8.Table
 var table16 *crc16.Table
 
-func FLACEncoder(codec *core.Codec, handler core.HandlerFunc) core.HandlerFunc {
-	if codec.Channels >= 2 {
-		return nil
-	}
-
+func FLACEncoder(codecName string, clockRate uint32, handler core.HandlerFunc) core.HandlerFunc {
 	var sr byte
-	switch codec.ClockRate {
+	switch clockRate {
 	case 8000:
 		sr = 0b0100
 	case 16000:
@@ -87,7 +83,7 @@ func FLACEncoder(codec *core.Codec, handler core.HandlerFunc) core.HandlerFunc {
 	return func(packet *rtp.Packet) {
 		samples := uint16(len(packet.Payload))
 
-		if codec.Name == core.CodecPCM || codec.Name == core.CodecPCML {
+		if codecName == core.CodecPCM || codecName == core.CodecPCML {
 			samples /= 2
 		}
 
@@ -115,7 +111,7 @@ func FLACEncoder(codec *core.Codec, handler core.HandlerFunc) core.HandlerFunc {
 		n += 1
 
 		// 3. Subframe
-		switch codec.Name {
+		switch codecName {
 		case core.CodecPCMA:
 			for _, b := range packet.Payload {
 				s16 := PCMAtoPCM(b)
diff --git a/pkg/pcm/pcm.go b/pkg/pcm/pcm.go
index 920dfd1d..60062b62 100644
--- a/pkg/pcm/pcm.go
+++ b/pkg/pcm/pcm.go
@@ -11,6 +11,10 @@ import (
 func ResampleToG711(codec *core.Codec, sampleRate uint32, handler core.HandlerFunc) core.HandlerFunc {
 	n := float32(codec.ClockRate) / float32(sampleRate)
 
+	if codec.Channels == 2 {
+		n *= 2 // hacky way for support two channels audio
+	}
+
 	switch codec.Name {
 	case core.CodecPCMA:
 		return DownsampleByte(PCMAtoPCM, PCMtoPCMA, n, handler)