From c2a398211c054b6e9a296df4c580b8a40399886e Mon Sep 17 00:00:00 2001
From: Alexey Khit <alexey.khit@gmail.com>
Date: Tue, 4 Jul 2023 12:06:11 +0300
Subject: [PATCH] Rewrite repack G711 func (for RTSP backchannel)

---
 pkg/pcm/helpers.go   | 44 -------------------------------------
 pkg/pcm/pcm.go       | 52 ++++++++++++++++++++++++++++++++++++++++++++
 pkg/rtsp/consumer.go |  4 ++--
 3 files changed, 54 insertions(+), 46 deletions(-)
 delete mode 100644 pkg/pcm/helpers.go

diff --git a/pkg/pcm/helpers.go b/pkg/pcm/helpers.go
deleted file mode 100644
index f2e723d5..00000000
--- a/pkg/pcm/helpers.go
+++ /dev/null
@@ -1,44 +0,0 @@
-package pcm
-
-import (
-	"github.com/AlexxIT/go2rtc/pkg/core"
-	"github.com/pion/rtp"
-	"sync"
-)
-
-func RepackBackchannel(handler core.HandlerFunc) core.HandlerFunc {
-	var buf []byte
-	var seq uint16
-
-	// fix https://github.com/AlexxIT/go2rtc/issues/432
-	var mu sync.Mutex
-
-	return func(packet *rtp.Packet) {
-		mu.Lock()
-
-		buf = append(buf, packet.Payload...)
-		if len(buf) < 1024 {
-			mu.Unlock()
-			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],
-		}
-
-		buf = buf[1024:]
-		seq++
-
-		mu.Unlock()
-
-		handler(pkt)
-	}
-}
diff --git a/pkg/pcm/pcm.go b/pkg/pcm/pcm.go
index 717a1450..d2c08717 100644
--- a/pkg/pcm/pcm.go
+++ b/pkg/pcm/pcm.go
@@ -3,6 +3,7 @@ package pcm
 import (
 	"github.com/AlexxIT/go2rtc/pkg/core"
 	"github.com/pion/rtp"
+	"sync"
 )
 
 func Resample(codec *core.Codec, sampleRate uint32, handler core.HandlerFunc) core.HandlerFunc {
@@ -114,3 +115,54 @@ func DownsamplePCM(fromPCM func(int16) byte, n float32, handler core.HandlerFunc
 		handler(&clone)
 	}
 }
+
+// RepackG711 - Repack G.711 PCMA/PCMU into frames of size 1024
+//  1. Fixes WebRTC audio quality issue (monotonic timestamp)
+//  2. Fixes Reolink Doorbell backchannel issue (zero timestamp)
+//     https://github.com/AlexxIT/go2rtc/issues/331
+func RepackG711(zeroTS bool, handler core.HandlerFunc) core.HandlerFunc {
+	const PacketSize = 1024
+
+	var buf []byte
+	var seq uint16
+	var ts uint32
+
+	// fix https://github.com/AlexxIT/go2rtc/issues/432
+	var mu sync.Mutex
+
+	return func(packet *rtp.Packet) {
+		mu.Lock()
+
+		buf = append(buf, packet.Payload...)
+		if len(buf) < PacketSize {
+			mu.Unlock()
+			return
+		}
+
+		pkt := &rtp.Packet{
+			Header: rtp.Header{
+				Version:        2,
+				Marker:         true,               // should be true
+				PayloadType:    packet.PayloadType, // will be owerwriten
+				SequenceNumber: seq,
+				SSRC:           packet.SSRC,
+			},
+			Payload: buf[:PacketSize],
+		}
+
+		seq++
+
+		// don't know if zero TS important for Reolink Doorbell
+		// don't have this strange devices for tests
+		if !zeroTS {
+			pkt.Timestamp = ts
+			ts += PacketSize
+		}
+
+		buf = buf[PacketSize:]
+
+		mu.Unlock()
+
+		handler(pkt)
+	}
+}
diff --git a/pkg/rtsp/consumer.go b/pkg/rtsp/consumer.go
index 903967c1..a0cc9662 100644
--- a/pkg/rtsp/consumer.go
+++ b/pkg/rtsp/consumer.go
@@ -62,9 +62,9 @@ func (c *Conn) AddTrack(media *core.Media, codec *core.Codec, track *core.Receiv
 	// 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)
+		// Fix Reolink Doorbell https://github.com/AlexxIT/go2rtc/issues/331
+		sender.Handler = pcm.RepackG711(true, sender.Handler)
 	}
 
 	sender.HandleRTP(track)