From 6d9d89bbe3ae0e90c8838412226d5aacbef922dc Mon Sep 17 00:00:00 2001
From: Alexey Khit <alexey.khit@gmail.com>
Date: Wed, 3 May 2023 08:01:33 +0300
Subject: [PATCH] Fix support 2 way audio for Reolink Doorbell #331

---
 pkg/pcm/helpers.go   | 35 +++++++++++++++++++++++++++++++++++
 pkg/rtsp/consumer.go |  7 +++++++
 2 files changed, 42 insertions(+)
 create mode 100644 pkg/pcm/helpers.go

diff --git a/pkg/pcm/helpers.go b/pkg/pcm/helpers.go
new file mode 100644
index 00000000..d873f7e3
--- /dev/null
+++ b/pkg/pcm/helpers.go
@@ -0,0 +1,35 @@
+package pcm
+
+import (
+	"github.com/AlexxIT/go2rtc/pkg/core"
+	"github.com/pion/rtp"
+)
+
+func RepackBackchannel(handler core.HandlerFunc) core.HandlerFunc {
+	var buf []byte
+	var seq uint16
+
+	return func(packet *rtp.Packet) {
+		buf = append(buf, packet.Payload...)
+		if len(buf) < 1024 {
+			return
+		}
+
+		pkt := &rtp.Packet{
+			Header: rtp.Header{
+				Version:        2,
+				Marker:         true,               // should be true
+				PayloadType:    packet.PayloadType, // will be owerwriten
+				SequenceNumber: seq,
+				Timestamp:      0, // should be always zero
+				SSRC:           packet.SSRC,
+			},
+			Payload: buf[:1024],
+		}
+
+		handler(pkt)
+
+		buf = buf[1024:]
+		seq++
+	}
+}
diff --git a/pkg/rtsp/consumer.go b/pkg/rtsp/consumer.go
index 38125147..663c8522 100644
--- a/pkg/rtsp/consumer.go
+++ b/pkg/rtsp/consumer.go
@@ -6,6 +6,7 @@ import (
 	"github.com/AlexxIT/go2rtc/pkg/h264"
 	"github.com/AlexxIT/go2rtc/pkg/h265"
 	"github.com/AlexxIT/go2rtc/pkg/mjpeg"
+	"github.com/AlexxIT/go2rtc/pkg/pcm"
 	"github.com/pion/rtp"
 	"time"
 )
@@ -60,6 +61,12 @@ func (c *Conn) AddTrack(media *core.Media, codec *core.Codec, track *core.Receiv
 	sender := core.NewSender(media, codec)
 	// important to send original codec for valid IsRTP check
 	sender.Handler = c.packetWriter(track.Codec, channel, codec.PayloadType)
+
+	// https://github.com/AlexxIT/go2rtc/issues/331
+	if c.mode == core.ModeActiveProducer && track.Codec.Name == core.CodecPCMA {
+		sender.Handler = pcm.RepackBackchannel(sender.Handler)
+	}
+
 	sender.HandleRTP(track)
 
 	c.senders = append(c.senders, sender)