Bolting on send side simulcast

Introduces AddEncoding method in RTP sender to add simulcast encodings.

Added UTs for AddEncoding.
Also modified the Simulcast send test to use the new API.

errors.go

@@ -142,6 +142,9 @@ var (
 	// ErrRTPSenderNewTrackHasIncorrectKind indicates that the new track is of a different kind than the previous/original
 	ErrRTPSenderNewTrackHasIncorrectKind = errors.New("new track must be of the same kind as previous")
 
+	// ErrRTPSenderNewTrackHasIncorrectEnvelope indicates that the new track has a different envelope than the previous/original
+	ErrRTPSenderNewTrackHasIncorrectEnvelope = errors.New("new track must have the same envelope as previous")
+
 	// ErrUnbindFailed indicates that a TrackLocal was not able to be unbind
 	ErrUnbindFailed = errors.New("failed to unbind TrackLocal from PeerConnection")
 
@@ -202,10 +205,16 @@ var (
 	errRTPReceiverWithSSRCTrackStreamNotFound = errors.New("unable to find stream for Track with SSRC")
 	errRTPReceiverForRIDTrackStreamNotFound   = errors.New("no trackStreams found for RID")
 
-	errRTPSenderTrackNil          = errors.New("Track must not be nil")
+	errRTPSenderTrackNil             = errors.New("Track must not be nil")
-	errRTPSenderDTLSTransportNil  = errors.New("DTLSTransport must not be nil")
+	errRTPSenderDTLSTransportNil     = errors.New("DTLSTransport must not be nil")
-	errRTPSenderSendAlreadyCalled = errors.New("Send has already been called")
+	errRTPSenderSendAlreadyCalled    = errors.New("Send has already been called")
-	errRTPSenderTrackRemoved      = errors.New("Sender Track has been removed or replaced to nil")
+	errRTPSenderStopped              = errors.New("Sender has already been stopped")
+	errRTPSenderTrackRemoved         = errors.New("Sender Track has been removed or replaced to nil")
+	errRTPSenderRidNil               = errors.New("Sender cannot add encoding as rid is empty")
+	errRTPSenderNoBaseEncoding       = errors.New("Sender cannot add encoding as there is no base track")
+	errRTPSenderBaseEncodingMismatch = errors.New("Sender cannot add encoding as provided track does not match base track")
+	errRTPSenderRIDCollision         = errors.New("Sender cannot encoding due to RID collision")
+	errRTPSenderNoTrackForRID        = errors.New("Sender does not have track for RID")
 
 	errRTPTransceiverCannotChangeMid        = errors.New("errRTPSenderTrackNil")
 	errRTPTransceiverSetSendingInvalidState = errors.New("invalid state change in RTPTransceiver.setSending")

peerconnection_media_test.go

@@ -162,7 +162,7 @@ func TestPeerConnection_Media_Sample(t *testing.T) {
 	go func() {
 		for {
 			time.Sleep(time.Millisecond * 100)
-			if routineErr := pcOffer.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{SenderSSRC: uint32(sender.ssrc), MediaSSRC: uint32(sender.ssrc)}}); routineErr != nil {
+			if routineErr := pcOffer.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{SenderSSRC: uint32(sender.trackEncodings[0].ssrc), MediaSSRC: uint32(sender.trackEncodings[0].ssrc)}}); routineErr != nil {
 				awaitRTCPSenderSend <- routineErr
 			}
 
@@ -643,12 +643,12 @@ func TestAddTransceiverAddTrack_Reuse(t *testing.T) {
 	track1, sender1 := addTrack()
 	assert.Equal(t, 1, len(pc.GetTransceivers()))
 	assert.Equal(t, sender1, tr.Sender())
-	assert.Equal(t, track1, tr.Sender().track)
+	assert.Equal(t, track1, tr.Sender().Track())
 	require.NoError(t, pc.RemoveTrack(sender1))
 
 	track2, _ := addTrack()
 	assert.Equal(t, 1, len(pc.GetTransceivers()))
-	assert.Equal(t, track2, tr.Sender().track)
+	assert.Equal(t, track2, tr.Sender().Track())
 
 	addTrack()
 	assert.Equal(t, 2, len(pc.GetTransceivers()))
@@ -1256,23 +1256,47 @@ func TestPeerConnection_Simulcast(t *testing.T) {
 		pcOffer, pcAnswer, err := NewAPI(WithMediaEngine(m)).newPair(Configuration{})
 		assert.NoError(t, err)
 
-		vp8Writer, err := NewTrackLocalStaticRTP(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion2")
+		vp8WriterA, err := NewTrackLocalStaticRTP(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion2", WithRTPStreamID("a"))
 		assert.NoError(t, err)
 
-		_, err = pcOffer.AddTrack(vp8Writer)
+		sender, err := pcOffer.AddTrack(vp8WriterA)
+		assert.NoError(t, err)
+		assert.NotNil(t, sender)
+
+		vp8WriterB, err := NewTrackLocalStaticRTP(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion2", WithRTPStreamID("b"))
+		assert.NoError(t, err)
+		err = sender.AddEncoding(vp8WriterB)
+		assert.NoError(t, err)
+
+		vp8WriterC, err := NewTrackLocalStaticRTP(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion2", WithRTPStreamID("c"))
+		assert.NoError(t, err)
+		err = sender.AddEncoding(vp8WriterC)
 		assert.NoError(t, err)
 
 		ridMap = map[string]int{}
 		pcAnswer.OnTrack(onTrackHandler)
 
-		assert.NoError(t, signalPairWithModification(pcOffer, pcAnswer, func(sessionDescription string) string {
+		parameters := sender.GetParameters()
-			sessionDescription = strings.Split(sessionDescription, "a=end-of-candidates\r\n")[0]
+		assert.Equal(t, "a", parameters.Encodings[0].RID)
-			sessionDescription = filterSsrc(sessionDescription)
+		assert.Equal(t, "b", parameters.Encodings[1].RID)
-			for _, rid := range rids {
+		assert.Equal(t, "c", parameters.Encodings[2].RID)
-				sessionDescription += "a=" + sdpAttributeRid + ":" + rid + " send\r\n"
+
+		var midID, ridID, rsidID uint8
+		for _, extension := range parameters.HeaderExtensions {
+			switch extension.URI {
+			case sdp.SDESMidURI:
+				midID = uint8(extension.ID)
+			case sdp.SDESRTPStreamIDURI:
+				ridID = uint8(extension.ID)
+			case sdesRepairRTPStreamIDURI:
+				rsidID = uint8(extension.ID)
 			}
-			return sessionDescription + "a=simulcast:send " + strings.Join(rids, ";") + "\r\n"
+		}
-		}))
+		assert.NotZero(t, midID)
+		assert.NotZero(t, ridID)
+		assert.NotZero(t, rsidID)
+
+		assert.NoError(t, signalPair(pcOffer, pcAnswer))
 
 		for sequenceNumber := uint16(0); !ridsFullfilled(); sequenceNumber++ {
 			time.Sleep(20 * time.Millisecond)
@@ -1284,17 +1308,26 @@ func TestPeerConnection_Simulcast(t *testing.T) {
 					SequenceNumber: sequenceNumber,
 					PayloadType:    96,
 				}
-				assert.NoError(t, header.SetExtension(1, []byte("0")))
+				assert.NoError(t, header.SetExtension(midID, []byte("0")))
 
 				// Send RSID for first 10 packets
 				if sequenceNumber >= 10 {
-					assert.NoError(t, header.SetExtension(2, []byte(rid)))
+					assert.NoError(t, header.SetExtension(ridID, []byte(rid)))
 				} else {
-					assert.NoError(t, header.SetExtension(3, []byte(rid)))
+					assert.NoError(t, header.SetExtension(rsidID, []byte(rid)))
 					header.SSRC += 10
 				}
 
-				_, err := vp8Writer.bindings[0].writeStream.WriteRTP(header, []byte{0x00})
+				var writer *TrackLocalStaticRTP
+				switch rid {
+				case "a":
+					writer = vp8WriterA
+				case "b":
+					writer = vp8WriterB
+				case "c":
+					writer = vp8WriterC
+				}
+				_, err = writer.bindings[0].writeStream.WriteRTP(header, []byte{0x00})
 				assert.NoError(t, err)
 			}
 		}

peerconnection_renegotiation_test.go

@@ -371,7 +371,7 @@ func TestPeerConnection_Transceiver_Mid(t *testing.T) {
 	// Must have 3 media descriptions (2 video channels)
 	assert.Equal(t, len(offer.parsed.MediaDescriptions), 2)
 
-	assert.True(t, sdpMidHasSsrc(offer, "0", sender1.ssrc), "Expected mid %q with ssrc %d, offer.SDP: %s", "0", sender1.ssrc, offer.SDP)
+	assert.True(t, sdpMidHasSsrc(offer, "0", sender1.trackEncodings[0].ssrc), "Expected mid %q with ssrc %d, offer.SDP: %s", "0", sender1.trackEncodings[0].ssrc, offer.SDP)
 
 	// Remove first track, must keep same number of media
 	// descriptions and same track ssrc for mid 1 as previous
@@ -382,7 +382,7 @@ func TestPeerConnection_Transceiver_Mid(t *testing.T) {
 
 	assert.Equal(t, len(offer.parsed.MediaDescriptions), 2)
 
-	assert.True(t, sdpMidHasSsrc(offer, "1", sender2.ssrc), "Expected mid %q with ssrc %d, offer.SDP: %s", "1", sender2.ssrc, offer.SDP)
+	assert.True(t, sdpMidHasSsrc(offer, "1", sender2.trackEncodings[0].ssrc), "Expected mid %q with ssrc %d, offer.SDP: %s", "1", sender2.trackEncodings[0].ssrc, offer.SDP)
 
 	_, err = pcAnswer.CreateAnswer(nil)
 	assert.Equal(t, err, &rtcerr.InvalidStateError{Err: ErrIncorrectSignalingState})
@@ -402,8 +402,8 @@ func TestPeerConnection_Transceiver_Mid(t *testing.T) {
 	// We reuse the existing non-sending transceiver
 	assert.Equal(t, len(offer.parsed.MediaDescriptions), 2)
 
-	assert.True(t, sdpMidHasSsrc(offer, "0", sender3.ssrc), "Expected mid %q with ssrc %d, offer.sdp: %s", "0", sender3.ssrc, offer.SDP)
+	assert.True(t, sdpMidHasSsrc(offer, "0", sender3.trackEncodings[0].ssrc), "Expected mid %q with ssrc %d, offer.sdp: %s", "0", sender3.trackEncodings[0].ssrc, offer.SDP)
-	assert.True(t, sdpMidHasSsrc(offer, "1", sender2.ssrc), "Expected mid %q with ssrc %d, offer.sdp: %s", "1", sender2.ssrc, offer.SDP)
+	assert.True(t, sdpMidHasSsrc(offer, "1", sender2.trackEncodings[0].ssrc), "Expected mid %q with ssrc %d, offer.sdp: %s", "1", sender2.trackEncodings[0].ssrc, offer.SDP)
 
 	closePairNow(t, pcOffer, pcAnswer)
 }

rtpsender.go

@@ -4,6 +4,7 @@
 package webrtc
 
 import (
+	"fmt"
 	"io"
 	"sync"
 	"time"
@@ -12,23 +13,30 @@ import (
 	"github.com/pion/randutil"
 	"github.com/pion/rtcp"
 	"github.com/pion/rtp"
+	"github.com/pion/webrtc/v3/internal/util"
 )
 
-// RTPSender allows an application to control how a given Track is encoded and transmitted to a remote peer
+type trackEncoding struct {
-type RTPSender struct {
 	track TrackLocal
 
-	srtpStream      *srtpWriterFuture
+	srtpStream *srtpWriterFuture
+
 	rtcpInterceptor interceptor.RTCPReader
 	streamInfo      interceptor.StreamInfo
 
 	context TrackLocalContext
 
+	ssrc SSRC
+}
+
+// RTPSender allows an application to control how a given Track is encoded and transmitted to a remote peer
+type RTPSender struct {
+	trackEncodings []*trackEncoding
+
 	transport *DTLSTransport
 
 	payloadType PayloadType
 	kind        RTPCodecType
-	ssrc        SSRC
 
 	// nolint:godox
 	// TODO(sgotti) remove this when in future we'll avoid replacing
@@ -60,23 +68,15 @@ func (api *API) NewRTPSender(track TrackLocal, transport *DTLSTransport) (*RTPSe
 	}
 
 	r := &RTPSender{
-		track:      track,
 		transport:  transport,
 		api:        api,
 		sendCalled: make(chan struct{}),
 		stopCalled: make(chan struct{}),
-		ssrc:       SSRC(randutil.NewMathRandomGenerator().Uint32()),
 		id:         id,
-		srtpStream: &srtpWriterFuture{},
 		kind:       track.Kind(),
 	}
 
-	r.srtpStream.rtpSender = r
+	r.addEncoding(track)
-
-	r.rtcpInterceptor = r.api.interceptor.BindRTCPReader(interceptor.RTPReaderFunc(func(in []byte, a interceptor.Attributes) (n int, attributes interceptor.Attributes, err error) {
-		n, err = r.srtpStream.Read(in)
-		return n, a, err
-	}))
 
 	return r, nil
 }
@@ -108,24 +108,26 @@ func (r *RTPSender) Transport() *DTLSTransport {
 }
 
 func (r *RTPSender) getParameters() RTPSendParameters {
-	var rid string
+	var encodings []RTPEncodingParameters
-	if r.track != nil {
+	for _, trackEncoding := range r.trackEncodings {
-		rid = r.track.RID()
+		var rid string
+		if trackEncoding.track != nil {
+			rid = trackEncoding.track.RID()
+		}
+		encodings = append(encodings, RTPEncodingParameters{
+			RTPCodingParameters: RTPCodingParameters{
+				RID:         rid,
+				SSRC:        trackEncoding.ssrc,
+				PayloadType: r.payloadType,
+			},
+		})
 	}
 	sendParameters := RTPSendParameters{
 		RTPParameters: r.api.mediaEngine.getRTPParametersByKind(
 			r.kind,
 			[]RTPTransceiverDirection{RTPTransceiverDirectionSendonly},
 		),
-		Encodings: []RTPEncodingParameters{
+		Encodings: encodings,
-			{
-				RTPCodingParameters: RTPCodingParameters{
-					RID:         rid,
-					SSRC:        r.ssrc,
-					PayloadType: r.payloadType,
-				},
-			},
-		},
 	}
 	if r.rtpTransceiver != nil {
 		sendParameters.Codecs = r.rtpTransceiver.getCodecs()
@@ -143,11 +145,81 @@ func (r *RTPSender) GetParameters() RTPSendParameters {
 	return r.getParameters()
 }
 
+// AddEncoding adds an encoding to RTPSender. Used by simulcast senders.
+func (r *RTPSender) AddEncoding(track TrackLocal) error {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if track == nil {
+		return errRTPSenderTrackNil
+	}
+
+	if track.RID() == "" {
+		return errRTPSenderRidNil
+	}
+
+	if r.hasStopped() {
+		return errRTPSenderStopped
+	}
+
+	if r.hasSent() {
+		return errRTPSenderSendAlreadyCalled
+	}
+
+	var refTrack TrackLocal
+	if len(r.trackEncodings) != 0 {
+		refTrack = r.trackEncodings[0].track
+	}
+	if refTrack == nil || refTrack.RID() == "" {
+		return errRTPSenderNoBaseEncoding
+	}
+
+	if refTrack.ID() != track.ID() || refTrack.StreamID() != track.StreamID() || refTrack.Kind() != track.Kind() {
+		return errRTPSenderBaseEncodingMismatch
+	}
+
+	for _, encoding := range r.trackEncodings {
+		if encoding.track == nil {
+			continue
+		}
+
+		if encoding.track.RID() == track.RID() {
+			return errRTPSenderRIDCollision
+		}
+	}
+
+	r.addEncoding(track)
+	return nil
+}
+
+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
+		}),
+	)
+
+	r.trackEncodings = append(r.trackEncodings, trackEncoding)
+}
+
 // Track returns the RTCRtpTransceiver track, or nil
 func (r *RTPSender) Track() TrackLocal {
 	r.mu.RLock()
 	defer r.mu.RUnlock()
-	return r.track
+
+	if len(r.trackEncodings) == 0 {
+		return nil
+	}
+
+	return r.trackEncodings[0].track
 }
 
 // ReplaceTrack replaces the track currently being used as the sender's source with a new TrackLocal.
@@ -161,26 +233,38 @@ func (r *RTPSender) ReplaceTrack(track TrackLocal) error {
 		return ErrRTPSenderNewTrackHasIncorrectKind
 	}
 
-	if r.hasSent() && r.track != nil {
+	// cannot replace simulcast envelope
-		if err := r.track.Unbind(r.context); err != nil {
+	if track != nil && len(r.trackEncodings) > 1 {
+		return ErrRTPSenderNewTrackHasIncorrectEnvelope
+	}
+
+	var replacedTrack TrackLocal
+	var context *TrackLocalContext
+	if len(r.trackEncodings) != 0 {
+		replacedTrack = r.trackEncodings[0].track
+		context = &r.trackEncodings[0].context
+	}
+	if r.hasSent() && replacedTrack != nil {
+		if err := replacedTrack.Unbind(*context); err != nil {
 			return err
 		}
 	}
 
 	if !r.hasSent() || track == nil {
-		r.track = track
+		r.trackEncodings[0].track = track
 		return nil
 	}
 
 	codec, err := track.Bind(TrackLocalContext{
-		id:          r.context.id,
+		id:              context.id,
-		params:      r.api.mediaEngine.getRTPParametersByKind(track.Kind(), []RTPTransceiverDirection{RTPTransceiverDirectionSendonly}),
+		params:          r.api.mediaEngine.getRTPParametersByKind(track.Kind(), []RTPTransceiverDirection{RTPTransceiverDirectionSendonly}),
-		ssrc:        r.context.ssrc,
+		ssrc:            context.ssrc,
-		writeStream: r.context.writeStream,
+		writeStream:     context.writeStream,
+		rtcpInterceptor: context.rtcpInterceptor,
 	})
 	if err != nil {
 		// Re-bind the original track
-		if _, reBindErr := r.track.Bind(r.context); reBindErr != nil {
+		if _, reBindErr := replacedTrack.Bind(*context); reBindErr != nil {
 			return reBindErr
 		}
 
@@ -189,10 +273,10 @@ func (r *RTPSender) ReplaceTrack(track TrackLocal) error {
 
 	// Codec has changed
 	if r.payloadType != codec.PayloadType {
-		r.context.params.Codecs = []RTPCodecParameters{codec}
+		context.params.Codecs = []RTPCodecParameters{codec}
 	}
 
-	r.track = track
+	r.trackEncodings[0].track = track
 	return nil
 }
 
@@ -204,29 +288,42 @@ func (r *RTPSender) Send(parameters RTPSendParameters) error {
 	switch {
 	case r.hasSent():
 		return errRTPSenderSendAlreadyCalled
-	case r.track == nil:
+	case r.trackEncodings[0].track == nil:
 		return errRTPSenderTrackRemoved
 	}
 
-	writeStream := &interceptorToTrackLocalWriter{}
+	for idx, trackEncoding := range r.trackEncodings {
-	r.context = TrackLocalContext{
+		writeStream := &interceptorToTrackLocalWriter{}
-		id:          r.id,
+		trackEncoding.context = TrackLocalContext{
-		params:      r.api.mediaEngine.getRTPParametersByKind(r.track.Kind(), []RTPTransceiverDirection{RTPTransceiverDirectionSendonly}),
+			id:              r.id,
-		ssrc:        parameters.Encodings[0].SSRC,
+			params:          r.api.mediaEngine.getRTPParametersByKind(trackEncoding.track.Kind(), []RTPTransceiverDirection{RTPTransceiverDirectionSendonly}),
-		writeStream: writeStream,
+			ssrc:            parameters.Encodings[idx].SSRC,
-	}
+			writeStream:     writeStream,
+			rtcpInterceptor: trackEncoding.rtcpInterceptor,
+		}
 
-	codec, err := r.track.Bind(r.context)
+		codec, err := trackEncoding.track.Bind(trackEncoding.context)
-	if err != nil {
+		if err != nil {
-		return err
+			return err
-	}
+		}
-	r.context.params.Codecs = []RTPCodecParameters{codec}
+		trackEncoding.context.params.Codecs = []RTPCodecParameters{codec}
 
-	r.streamInfo = *createStreamInfo(r.id, parameters.Encodings[0].SSRC, codec.PayloadType, codec.RTPCodecCapability, parameters.HeaderExtensions)
+		trackEncoding.streamInfo = *createStreamInfo(
-	rtpInterceptor := r.api.interceptor.BindLocalStream(&r.streamInfo, interceptor.RTPWriterFunc(func(header *rtp.Header, payload []byte, attributes interceptor.Attributes) (int, error) {
+			r.id,
-		return r.srtpStream.WriteRTP(header, payload)
+			parameters.Encodings[idx].SSRC,
-	}))
+			codec.PayloadType,
-	writeStream.interceptor.Store(rtpInterceptor)
+			codec.RTPCodecCapability,
+			parameters.HeaderExtensions,
+		)
+		srtpStream := trackEncoding.srtpStream
+		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)
+	}
 
 	close(r.sendCalled)
 	return nil
@@ -252,16 +349,20 @@ func (r *RTPSender) Stop() error {
 		return err
 	}
 
-	r.api.interceptor.UnbindLocalStream(&r.streamInfo)
+	errs := []error{}
+	for _, trackEncoding := range r.trackEncodings {
+		r.api.interceptor.UnbindLocalStream(&trackEncoding.streamInfo)
+		errs = append(errs, trackEncoding.srtpStream.Close())
+	}
 
-	return r.srtpStream.Close()
+	return util.FlattenErrs(errs)
 }
 
-// Read reads incoming RTCP for this RTPReceiver
+// Read reads incoming RTCP for this RTPSender
 func (r *RTPSender) Read(b []byte) (n int, a interceptor.Attributes, err error) {
 	select {
 	case <-r.sendCalled:
-		return r.rtcpInterceptor.Read(b, a)
+		return r.trackEncodings[0].rtcpInterceptor.Read(b, a)
 	case <-r.stopCalled:
 		return 0, nil, io.ErrClosedPipe
 	}
@@ -283,10 +384,50 @@ func (r *RTPSender) ReadRTCP() ([]rtcp.Packet, interceptor.Attributes, error) {
 	return pkts, attributes, nil
 }
 
+// ReadSimulcast reads incoming RTCP for this RTPSender for given rid
+func (r *RTPSender) ReadSimulcast(b []byte, rid string) (n int, a interceptor.Attributes, err error) {
+	select {
+	case <-r.sendCalled:
+		for _, t := range r.trackEncodings {
+			if t.track != nil && t.track.RID() == rid {
+				return t.rtcpInterceptor.Read(b, a)
+			}
+		}
+		return 0, nil, fmt.Errorf("%w: %s", errRTPSenderNoTrackForRID, rid)
+	case <-r.stopCalled:
+		return 0, nil, io.ErrClosedPipe
+	}
+}
+
+// ReadSimulcastRTCP is a convenience method that wraps ReadSimulcast and unmarshal for you
+func (r *RTPSender) ReadSimulcastRTCP(rid string) ([]rtcp.Packet, interceptor.Attributes, error) {
+	b := make([]byte, r.api.settingEngine.getReceiveMTU())
+	i, attributes, err := r.ReadSimulcast(b, rid)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	pkts, err := rtcp.Unmarshal(b[:i])
+	return pkts, attributes, err
+}
+
 // SetReadDeadline sets the deadline for the Read operation.
 // Setting to zero means no deadline.
 func (r *RTPSender) SetReadDeadline(t time.Time) error {
-	return r.srtpStream.SetReadDeadline(t)
+	return r.trackEncodings[0].srtpStream.SetReadDeadline(t)
+}
+
+// SetReadDeadlineSimulcast sets the max amount of time the RTCP stream for a given rid will block before returning. 0 is forever.
+func (r *RTPSender) SetReadDeadlineSimulcast(deadline time.Time, rid string) error {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
+	for _, t := range r.trackEncodings {
+		if t.track != nil && t.track.RID() == rid {
+			return t.srtpStream.SetReadDeadline(deadline)
+		}
+	}
+	return fmt.Errorf("%w: %s", errRTPSenderNoTrackForRID, rid)
 }
 
 // hasSent tells if data has been ever sent for this instance

rtpsender_test.go

@@ -117,7 +117,7 @@ func Test_RTPSender_GetParameters(t *testing.T) {
 	parameters := rtpTransceiver.Sender().GetParameters()
 	assert.NotEqual(t, 0, len(parameters.Codecs))
 	assert.Equal(t, 1, len(parameters.Encodings))
-	assert.Equal(t, rtpTransceiver.Sender().ssrc, parameters.Encodings[0].SSRC)
+	assert.Equal(t, rtpTransceiver.Sender().trackEncodings[0].ssrc, parameters.Encodings[0].SSRC)
 	assert.Equal(t, "", parameters.Encodings[0].RID)
 
 	closePairNow(t, offerer, answerer)
@@ -340,3 +340,64 @@ func Test_RTPSender_Send_Track_Removed(t *testing.T) {
 
 	assert.NoError(t, peerConnection.Close())
 }
+
+func Test_RTPSender_Add_Encoding(t *testing.T) {
+	track, err := NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion")
+	assert.NoError(t, err)
+
+	peerConnection, err := NewPeerConnection(Configuration{})
+	assert.NoError(t, err)
+
+	rtpSender, err := peerConnection.AddTrack(track)
+	assert.NoError(t, err)
+
+	assert.Equal(t, errRTPSenderTrackNil, rtpSender.AddEncoding(nil))
+
+	track1, err := NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion")
+	assert.NoError(t, err)
+	assert.Equal(t, errRTPSenderRidNil, rtpSender.AddEncoding(track1))
+
+	track1, err = NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion", WithRTPStreamID("h"))
+	assert.NoError(t, err)
+	assert.Equal(t, errRTPSenderNoBaseEncoding, rtpSender.AddEncoding(track1))
+
+	track, err = NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion", WithRTPStreamID("q"))
+	assert.NoError(t, err)
+
+	rtpSender, err = peerConnection.AddTrack(track)
+	assert.NoError(t, err)
+
+	track1, err = NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video1", "pion", WithRTPStreamID("h"))
+	assert.NoError(t, err)
+	assert.Equal(t, errRTPSenderBaseEncodingMismatch, rtpSender.AddEncoding(track1))
+
+	track1, err = NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion1", WithRTPStreamID("h"))
+	assert.NoError(t, err)
+	assert.Equal(t, errRTPSenderBaseEncodingMismatch, rtpSender.AddEncoding(track1))
+
+	track1, err = NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeOpus}, "video", "pion", WithRTPStreamID("h"))
+	assert.NoError(t, err)
+	assert.Equal(t, errRTPSenderBaseEncodingMismatch, rtpSender.AddEncoding(track1))
+
+	track1, err = NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion", WithRTPStreamID("q"))
+	assert.NoError(t, err)
+	assert.Equal(t, errRTPSenderRIDCollision, rtpSender.AddEncoding(track1))
+
+	track1, err = NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion", WithRTPStreamID("h"))
+	assert.NoError(t, err)
+	assert.NoError(t, rtpSender.AddEncoding(track1))
+
+	err = rtpSender.Send(rtpSender.GetParameters())
+	assert.NoError(t, err)
+
+	track1, err = NewTrackLocalStaticSample(RTPCodecCapability{MimeType: MimeTypeVP8}, "video", "pion", WithRTPStreamID("f"))
+	assert.NoError(t, err)
+	assert.Equal(t, errRTPSenderSendAlreadyCalled, rtpSender.AddEncoding(track1))
+
+	err = rtpSender.Stop()
+	assert.NoError(t, err)
+
+	assert.Equal(t, errRTPSenderStopped, rtpSender.AddEncoding(track1))
+
+	assert.NoError(t, peerConnection.Close())
+}

sdp.go

@@ -340,7 +340,60 @@ func populateLocalCandidates(sessionDescription *SessionDescription, i *ICEGathe
 	}
 }
 
-func addTransceiverSDP(d *sdp.SessionDescription, isPlanB, shouldAddCandidates bool, dtlsFingerprints []DTLSFingerprint, mediaEngine *MediaEngine, midValue string, iceParams ICEParameters, candidates []ICECandidate, dtlsRole sdp.ConnectionRole, iceGatheringState ICEGatheringState, mediaSection mediaSection) (bool, error) {
+func addSenderSDP(
+	mediaSection mediaSection,
+	isPlanB bool,
+	media *sdp.MediaDescription,
+) {
+	for _, mt := range mediaSection.transceivers {
+		sender := mt.Sender()
+		if sender == nil {
+			continue
+		}
+
+		track := sender.Track()
+		if track == nil {
+			continue
+		}
+
+		sendParameters := sender.GetParameters()
+		for _, encoding := range sendParameters.Encodings {
+			media = media.WithMediaSource(uint32(encoding.SSRC), track.StreamID() /* cname */, track.StreamID() /* streamLabel */, track.ID())
+			if !isPlanB {
+				media = media.WithPropertyAttribute("msid:" + track.StreamID() + " " + track.ID())
+			}
+		}
+
+		if len(sendParameters.Encodings) > 1 {
+			sendRids := make([]string, 0, len(sendParameters.Encodings))
+
+			for _, encoding := range sendParameters.Encodings {
+				media.WithValueAttribute(sdpAttributeRid, encoding.RID+" send")
+				sendRids = append(sendRids, encoding.RID)
+			}
+			// Simulcast
+			media.WithValueAttribute("simulcast", "send "+strings.Join(sendRids, ";"))
+		}
+
+		if !isPlanB {
+			break
+		}
+	}
+}
+
+func addTransceiverSDP(
+	d *sdp.SessionDescription,
+	isPlanB bool,
+	shouldAddCandidates bool,
+	dtlsFingerprints []DTLSFingerprint,
+	mediaEngine *MediaEngine,
+	midValue string,
+	iceParams ICEParameters,
+	candidates []ICECandidate,
+	dtlsRole sdp.ConnectionRole,
+	iceGatheringState ICEGatheringState,
+	mediaSection mediaSection,
+) (bool, error) {
 	transceivers := mediaSection.transceivers
 	if len(transceivers) < 1 {
 		return false, errSDPZeroTransceivers
@@ -410,16 +463,7 @@ func addTransceiverSDP(d *sdp.SessionDescription, isPlanB, shouldAddCandidates b
 		media.WithValueAttribute("simulcast", "recv "+strings.Join(recvRids, ";"))
 	}
 
-	for _, mt := range transceivers {
+	addSenderSDP(mediaSection, isPlanB, media)
-		if sender := mt.Sender(); sender != nil && sender.Track() != nil {
-			track := sender.Track()
-			media = media.WithMediaSource(uint32(sender.ssrc), track.StreamID() /* cname */, track.StreamID() /* streamLabel */, track.ID())
-			if !isPlanB {
-				media = media.WithPropertyAttribute("msid:" + track.StreamID() + " " + track.ID())
-				break
-			}
-		}
-	}
 
 	media = media.WithPropertyAttribute(t.Direction().String())
 

srtp_writer_future.go

@@ -16,6 +16,7 @@ import (
 // srtpWriterFuture blocks Read/Write calls until
 // the SRTP Session is available
 type srtpWriterFuture struct {
+	ssrc           SSRC
 	rtpSender      *RTPSender
 	rtcpReadStream atomic.Value // *srtp.ReadStreamSRTCP
 	rtpWriteStream atomic.Value // *srtp.WriteStreamSRTP
@@ -52,7 +53,7 @@ func (s *srtpWriterFuture) init(returnWhenNoSRTP bool) error {
 		return err
 	}
 
-	rtcpReadStream, err := srtcpSession.OpenReadStream(uint32(s.rtpSender.ssrc))
+	rtcpReadStream, err := srtcpSession.OpenReadStream(uint32(s.ssrc))
 	if err != nil {
 		return err
 	}

track_local.go

@@ -1,6 +1,9 @@
 package webrtc
 
-import "github.com/pion/rtp"
+import (
+	"github.com/pion/interceptor"
+	"github.com/pion/rtp"
+)
 
 // TrackLocalWriter is the Writer for outbound RTP Packets
 type TrackLocalWriter interface {
@@ -14,10 +17,11 @@ type TrackLocalWriter interface {
 // TrackLocalContext is the Context passed when a TrackLocal has been Binded/Unbinded from a PeerConnection, and used
 // in Interceptors.
 type TrackLocalContext struct {
-	id          string
+	id              string
-	params      RTPParameters
+	params          RTPParameters
-	ssrc        SSRC
+	ssrc            SSRC
-	writeStream TrackLocalWriter
+	writeStream     TrackLocalWriter
+	rtcpInterceptor interceptor.RTCPReader
 }
 
 // CodecParameters returns the negotiated RTPCodecParameters. These are the codecs supported by both
@@ -49,6 +53,11 @@ func (t *TrackLocalContext) ID() string {
 	return t.id
 }
 
+// RTCPReader returns the RTCP interceptor for this TrackLocal. Used to read RTCP of this TrackLocal.
+func (t *TrackLocalContext) RTCPReader() interceptor.RTCPReader {
+	return t.rtcpInterceptor
+}
+
 // TrackLocal is an interface that controls how the user can send media
 // The user can provide their own TrackLocal implementations, or use
 // the implementations in pkg/media