Respect SSRC Choice by User

Respect SSRC chosen via RTPTransceiverInit

AUTHORS.txt

@@ -137,6 +137,7 @@ Michael MacDonald <github@macdonald.cx>
 Michael MacDonald <mike.macdonald@savantsystems.com>
 Michiel De Backker <38858977+backkem@users.noreply.github.com>
 Mike Coleman <mc@fivebats.com>
+Mikhail <mvrogushkov@sberbank.ru>
 Mindgamesnl <matsmoolhuizen@gmail.com>
 mission-liao <missionaryliao@gmail.com>
 mohammadne <mohammadne@mail.ru>

peerconnection.go

@@ -1865,7 +1865,7 @@ func (pc *PeerConnection) RemoveTrack(sender *RTPSender) (err error) {
 	return
 }
 
-func (pc *PeerConnection) newTransceiverFromTrack(direction RTPTransceiverDirection, track TrackLocal) (t *RTPTransceiver, err error) {
+func (pc *PeerConnection) newTransceiverFromTrack(direction RTPTransceiverDirection, track TrackLocal, init ...RTPTransceiverInit) (t *RTPTransceiver, err error) {
 	var (
 		r *RTPReceiver
 		s *RTPSender
@@ -1885,6 +1885,13 @@ func (pc *PeerConnection) newTransceiverFromTrack(direction RTPTransceiverDirect
 	if err != nil {
 		return
 	}
+
+	// Allow RTPTransceiverInit to override SSRC
+	if s != nil && len(s.trackEncodings) == 1 &&
+		len(init) == 1 && len(init[0].SendEncodings) == 1 && init[0].SendEncodings[0].SSRC != 0 {
+		s.trackEncodings[0].ssrc = init[0].SendEncodings[0].SSRC
+	}
+
 	return newRTPTransceiver(r, s, direction, track.Kind(), pc.api), nil
 }
 
@@ -1910,7 +1917,7 @@ func (pc *PeerConnection) AddTransceiverFromKind(kind RTPCodecType, init ...RTPT
 		if err != nil {
 			return nil, err
 		}
-		t, err = pc.newTransceiverFromTrack(direction, track)
+		t, err = pc.newTransceiverFromTrack(direction, track, init...)
 		if err != nil {
 			return nil, err
 		}
@@ -1942,7 +1949,7 @@ func (pc *PeerConnection) AddTransceiverFromTrack(track TrackLocal, init ...RTPT
 		direction = init[0].Direction
 	}
 
-	t, err = pc.newTransceiverFromTrack(direction, track)
+	t, err = pc.newTransceiverFromTrack(direction, track, init...)
 	if err == nil {
 		pc.mu.Lock()
 		pc.addRTPTransceiver(t)

peerconnection_media_test.go

@@ -152,9 +152,11 @@ func TestPeerConnection_Media_Sample(t *testing.T) {
 	}()
 
 	go func() {
+		parameters := sender.GetParameters()
+
 		for {
 			time.Sleep(time.Millisecond * 100)
-			if routineErr := pcOffer.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{SenderSSRC: uint32(sender.trackEncodings[0].ssrc), MediaSSRC: uint32(sender.trackEncodings[0].ssrc)}}); routineErr != nil {
+			if routineErr := pcOffer.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{SenderSSRC: uint32(parameters.Encodings[0].SSRC), MediaSSRC: uint32(parameters.Encodings[0].SSRC)}}); routineErr != nil {
 				awaitRTCPSenderSend <- routineErr
 			}
 

rtpsender.go

@@ -111,6 +111,9 @@ func (r *RTPSender) Transport() *DTLSTransport {
 }
 
 func (r *RTPSender) getParameters() RTPSendParameters {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
 	var encodings []RTPEncodingParameters
 	for _, trackEncoding := range r.trackEncodings {
 		var rid string
@@ -196,19 +199,10 @@ func (r *RTPSender) AddEncoding(track TrackLocal) error {
 }
 
 func (r *RTPSender) addEncoding(track TrackLocal) {
-	ssrc := SSRC(randutil.NewMathRandomGenerator().Uint32())
 	trackEncoding := &trackEncoding{
-		track:      track,
-		srtpStream: &srtpWriterFuture{ssrc: ssrc},
-		ssrc:       ssrc,
-	}
-	trackEncoding.srtpStream.rtpSender = r
-	trackEncoding.rtcpInterceptor = r.api.interceptor.BindRTCPReader(
-		interceptor.RTPReaderFunc(func(in []byte, a interceptor.Attributes) (n int, attributes interceptor.Attributes, err error) {
-			n, err = trackEncoding.srtpStream.Read(in)
-			return n, a, err
-		}),
-	)
+		track: track,
+		ssrc:  SSRC(randutil.NewMathRandomGenerator().Uint32()),
+	}
 
 	r.trackEncodings = append(r.trackEncodings, trackEncoding)
 }
@@ -295,8 +289,13 @@ func (r *RTPSender) Send(parameters RTPSendParameters) error {
 		return errRTPSenderTrackRemoved
 	}
 
-	for idx, trackEncoding := range r.trackEncodings {
+	for idx := range r.trackEncodings {
+		trackEncoding := r.trackEncodings[idx]
+		srtpStream := &srtpWriterFuture{ssrc: parameters.Encodings[idx].SSRC, rtpSender: r}
 		writeStream := &interceptorToTrackLocalWriter{}
+
+		trackEncoding.srtpStream = srtpStream
+		trackEncoding.ssrc = parameters.Encodings[idx].SSRC
 		trackEncoding.context = &baseTrackLocalContext{
 			id:              r.id,
 			params:          r.api.mediaEngine.getRTPParametersByKind(trackEncoding.track.Kind(), []RTPTransceiverDirection{RTPTransceiverDirectionSendonly}),
@@ -318,13 +317,21 @@ func (r *RTPSender) Send(parameters RTPSendParameters) error {
 			codec.RTPCodecCapability,
 			parameters.HeaderExtensions,
 		)
-		srtpStream := trackEncoding.srtpStream
+
+		trackEncoding.rtcpInterceptor = r.api.interceptor.BindRTCPReader(
+			interceptor.RTPReaderFunc(func(in []byte, a interceptor.Attributes) (n int, attributes interceptor.Attributes, err error) {
+				n, err = trackEncoding.srtpStream.Read(in)
+				return n, a, err
+			}),
+		)
+
 		rtpInterceptor := r.api.interceptor.BindLocalStream(
 			&trackEncoding.streamInfo,
 			interceptor.RTPWriterFunc(func(header *rtp.Header, payload []byte, attributes interceptor.Attributes) (int, error) {
 				return srtpStream.WriteRTP(header, payload)
 			}),
 		)
+
 		writeStream.interceptor.Store(rtpInterceptor)
 	}
 
@@ -355,7 +362,9 @@ func (r *RTPSender) Stop() error {
 	errs := []error{}
 	for _, trackEncoding := range r.trackEncodings {
 		r.api.interceptor.UnbindLocalStream(&trackEncoding.streamInfo)
-		errs = append(errs, trackEncoding.srtpStream.Close())
+		if trackEncoding.srtpStream != nil {
+			errs = append(errs, trackEncoding.srtpStream.Close())
+		}
 	}
 
 	return util.FlattenErrs(errs)

rtptransceiverinit_go_test.go

@@ -0,0 +1,79 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+//go:build !js
+// +build !js
+
+package webrtc
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/pion/transport/v3/test"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_RTPTransceiverInit_SSRC(t *testing.T) {
+	lim := test.TimeOut(time.Second * 30) //nolint
+	defer lim.Stop()
+
+	report := test.CheckRoutines(t)
+	defer report()
+
+	track, err := NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeOpus}, "a", "b")
+	assert.NoError(t, err)
+
+	t.Run("SSRC of 0 is ignored", func(t *testing.T) {
+		offerer, answerer, err := newPair()
+		assert.NoError(t, err)
+
+		ctx, cancel := context.WithCancel(context.Background())
+		answerer.OnTrack(func(track *TrackRemote, _ *RTPReceiver) {
+			assert.NotEqual(t, 0, track.SSRC())
+			cancel()
+		})
+
+		_, err = offerer.AddTransceiverFromTrack(track, RTPTransceiverInit{
+			Direction: RTPTransceiverDirectionSendonly,
+			SendEncodings: []RTPEncodingParameters{
+				{
+					RTPCodingParameters: RTPCodingParameters{
+						SSRC: 0,
+					},
+				},
+			},
+		})
+		assert.NoError(t, err)
+		assert.NoError(t, signalPair(offerer, answerer))
+		sendVideoUntilDone(ctx.Done(), t, []*TrackLocalStaticSample{track})
+		closePairNow(t, offerer, answerer)
+	})
+
+	t.Run("SSRC of 5000", func(t *testing.T) {
+		offerer, answerer, err := newPair()
+		assert.NoError(t, err)
+
+		ctx, cancel := context.WithCancel(context.Background())
+		answerer.OnTrack(func(track *TrackRemote, _ *RTPReceiver) {
+			assert.NotEqual(t, 5000, track.SSRC())
+			cancel()
+		})
+
+		_, err = offerer.AddTransceiverFromTrack(track, RTPTransceiverInit{
+			Direction: RTPTransceiverDirectionSendonly,
+			SendEncodings: []RTPEncodingParameters{
+				{
+					RTPCodingParameters: RTPCodingParameters{
+						SSRC: 5000,
+					},
+				},
+			},
+		})
+		assert.NoError(t, err)
+		assert.NoError(t, signalPair(offerer, answerer))
+		sendVideoUntilDone(ctx.Done(), t, []*TrackLocalStaticSample{track})
+		closePairNow(t, offerer, answerer)
+	})
+}