From b617796941f7e139046d08f0c49c30a92c7acb5d Mon Sep 17 00:00:00 2001
From: Alexey Khit <alexey.khit@gmail.com>
Date: Sun, 13 Nov 2022 14:35:53 +0300
Subject: [PATCH] Improve RTCP for HomeKit

---
 cmd/srtp/srtp.go    |  9 +++----
 pkg/srtp/session.go | 57 +++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 56 insertions(+), 10 deletions(-)

diff --git a/cmd/srtp/srtp.go b/cmd/srtp/srtp.go
index 7f251ee4..a8e2c8b6 100644
--- a/cmd/srtp/srtp.go
+++ b/cmd/srtp/srtp.go
@@ -3,7 +3,6 @@ package srtp
 import (
 	"github.com/AlexxIT/go2rtc/cmd/app"
 	"github.com/AlexxIT/go2rtc/pkg/srtp"
-	"github.com/rs/zerolog"
 	"net"
 )
 
@@ -24,12 +23,12 @@ func Init() {
 		return
 	}
 
-	log = app.GetLogger("srtp")
+	log := app.GetLogger("srtp")
 
 	// create SRTP server (endpoint) for receiving video from HomeKit camera
 	conn, err := net.ListenPacket("udp", cfg.Mod.Listen)
 	if err != nil {
-		log.Warn().Err(err).Msg("[srtp] listen")
+		log.Warn().Err(err).Caller().Send()
 	}
 
 	log.Info().Str("addr", cfg.Mod.Listen).Msg("[srtp] listen")
@@ -38,11 +37,9 @@ func Init() {
 	go func() {
 		Server = &srtp.Server{}
 		if err = Server.Serve(conn); err != nil {
-			log.Warn().Err(err).Msg("[srtp] serve")
+			log.Warn().Err(err).Caller().Send()
 		}
 	}()
 }
 
 var Server *srtp.Server
-
-var log zerolog.Logger
diff --git a/pkg/srtp/session.go b/pkg/srtp/session.go
index 1bb8208d..07321396 100644
--- a/pkg/srtp/session.go
+++ b/pkg/srtp/session.go
@@ -5,6 +5,7 @@ import (
 	"github.com/pion/rtcp"
 	"github.com/pion/rtp"
 	"github.com/pion/srtp/v2"
+	"time"
 )
 
 type Session struct {
@@ -16,6 +17,14 @@ type Session struct {
 
 	Write func(b []byte) (int, error)
 	Track *streamer.Track
+
+	lastSequence  uint32
+	lastTimestamp uint32
+	//lastPacket    *rtp.Packet
+	lastTime time.Time
+	jitter   float64
+	//sequenceCycle uint16
+	totalLost uint32
 }
 
 func (s *Session) SetKeys(
@@ -46,8 +55,33 @@ func (s *Session) HandleRTP(data []byte) (err error) {
 		return
 	}
 
+	now := time.Now()
+
+	// https://www.ietf.org/rfc/rfc3550.txt
+	if s.lastTimestamp != 0 {
+		delta := packet.SequenceNumber - uint16(s.lastSequence)
+
+		// lost packet
+		if delta > 1 {
+			s.totalLost += uint32(delta - 1)
+		}
+
+		// D(i,j) = (Rj - Ri) - (Sj - Si) = (Rj - Sj) - (Ri - Si)
+		dTime := now.Sub(s.lastTime).Seconds()*float64(s.Track.Codec.ClockRate) -
+			float64(packet.Timestamp-s.lastTimestamp)
+		if dTime < 0 {
+			dTime = -dTime
+		}
+		// J(i) = J(i-1) + (|D(i-1,i)| - J(i-1))/16
+		s.jitter += (dTime - s.jitter) / 16
+	}
+
+	// keeping cycles (overflow)
+	s.lastSequence = s.lastSequence&0xFFFF0000 | uint32(packet.SequenceNumber)
+	s.lastTimestamp = packet.Timestamp
+	s.lastTime = now
+
 	_ = s.Track.WriteRTP(packet)
-	//s.Output(core.RTP{Channel: s.Channel, Packet: packet})
 
 	return
 }
@@ -64,7 +98,6 @@ func (s *Session) HandleRTCP(data []byte) (err error) {
 	}
 
 	_ = packets
-	//s.Output(core.RTCP{Channel: s.Channel + 1, Header: header, Packets: packets})
 
 	if header.Type == rtcp.TypeSenderReport {
 		err = s.KeepAlive()
@@ -74,9 +107,25 @@ func (s *Session) HandleRTCP(data []byte) (err error) {
 }
 
 func (s *Session) KeepAlive() (err error) {
-	var data []byte
-	// we can send empty receiver response, but should send it to hold the connection
 	rep := rtcp.ReceiverReport{SSRC: s.LocalSSRC}
+
+	if s.lastTimestamp > 0 {
+		//log.Printf("[RTCP] ssrc=%d seq=%d lost=%d jit=%.2f", s.RemoteSSRC, s.lastSequence, s.totalLost, s.jitter)
+
+		rep.Reports = []rtcp.ReceptionReport{{
+			SSRC:               s.RemoteSSRC,
+			LastSequenceNumber: s.lastSequence,
+			LastSenderReport:   s.lastTimestamp,
+			FractionLost:       0, // TODO
+			TotalLost:          s.totalLost,
+			Delay:              0, // send just after receive
+			Jitter:             uint32(s.jitter),
+		}}
+	}
+
+	// we can send empty receiver response, but should send it to hold the connection
+
+	var data []byte
 	if data, err = rep.Marshal(); err != nil {
 		return
 	}