Support TrackLocal RTX

rtpcodec.go

@@ -4,6 +4,8 @@
 package webrtc
 
 import (
+	"fmt"
+	"regexp"
 	"strings"
 
 	"github.com/pion/webrtc/v4/internal/fmtp"
@@ -123,3 +125,27 @@ func codecParametersFuzzySearch(needle RTPCodecParameters, haystack []RTPCodecPa
 
 	return RTPCodecParameters{}, codecMatchNone
 }
+
+// Do a fuzzy find for a associated codec in the list of codecs
+// Used for lookup up a associated codec in an existing list to find a match
+// Returns codecMatchExact, codecMatchPartial, or codecMatchNone
+func codecParametersAssociatedSearch(needle RTPCodecParameters, haystack []RTPCodecParameters) (RTPCodecParameters, codecMatchType) {
+
+	// First attempt to match Exact
+	for _, c := range haystack {
+		if c.SDPFmtpLine == fmt.Sprintf("apt=%d", needle.PayloadType) {
+			return c, codecMatchExact
+		}
+	}
+
+	// Fallback to just has apt codec
+	if re, err := regexp.Compile(`^apt=\d+$`); err == nil {
+		for _, c := range haystack {
+			if re.MatchString(c.SDPFmtpLine) {
+				return c, codecMatchPartial
+			}
+		}
+	}
+
+	return RTPCodecParameters{}, codecMatchNone
+}

rtpsender.go

@@ -20,16 +20,18 @@ import (
 )
 
 type trackEncoding struct {
-	track TrackLocal
-
-	srtpStream *srtpWriterFuture
+	track   TrackLocal
+	context *baseTrackLocalContext
 
+	ssrc            SSRC
+	srtpStream      *srtpWriterFuture
 	rtcpInterceptor interceptor.RTCPReader
 	streamInfo      interceptor.StreamInfo
 
-	context *baseTrackLocalContext
-
-	ssrc SSRC
+	rtxSsrc            SSRC
+	rtxSrtpStream      *srtpWriterFuture
+	rtxRtcpInterceptor interceptor.RTCPReader
+	rtxStreamInfo      interceptor.StreamInfo
 }
 
 // RTPSender allows an application to control how a given Track is encoded and transmitted to a remote peer
@@ -125,6 +127,7 @@ func (r *RTPSender) getParameters() RTPSendParameters {
 				RID:         rid,
 				SSRC:        trackEncoding.ssrc,
 				PayloadType: r.payloadType,
+				RTX:         RTPRtxParameters{SSRC: trackEncoding.rtxSsrc},
 			},
 		})
 	}
@@ -204,6 +207,16 @@ func (r *RTPSender) addEncoding(track TrackLocal) {
 		ssrc:  SSRC(randutil.NewMathRandomGenerator().Uint32()),
 	}
 
+	if r.api.settingEngine.trackLocalRtx {
+		codecs := r.api.mediaEngine.getCodecsByKind(track.Kind())
+		for _, c := range codecs {
+			if _, matchType := codecParametersAssociatedSearch(c, codecs); matchType != codecMatchNone {
+				trackEncoding.rtxSsrc = SSRC(randutil.NewMathRandomGenerator().Uint32())
+				break
+			}
+		}
+	}
+
 	r.trackEncodings = append(r.trackEncodings, trackEncoding)
 }
 
@@ -339,6 +352,38 @@ func (r *RTPSender) Send(parameters RTPSendParameters) error {
 		)
 
 		writeStream.interceptor.Store(rtpInterceptor)
+
+		if rtxCodec, matchType := codecParametersAssociatedSearch(codec, r.api.mediaEngine.getCodecsByKind(r.kind)); matchType == codecMatchExact &&
+			parameters.Encodings[idx].RTX.SSRC != 0 {
+
+			rtxSrtpStream := &srtpWriterFuture{ssrc: parameters.Encodings[idx].RTX.SSRC, rtpSender: r}
+
+			trackEncoding.rtxSrtpStream = rtxSrtpStream
+			trackEncoding.rtxSsrc = parameters.Encodings[idx].RTX.SSRC
+
+			trackEncoding.rtxStreamInfo = *createStreamInfo(
+				r.id+"_rtx",
+				parameters.Encodings[idx].RTX.SSRC,
+				rtxCodec.PayloadType,
+				rtxCodec.RTPCodecCapability,
+				parameters.HeaderExtensions,
+			)
+			trackEncoding.rtxStreamInfo.Attributes.Set("apt_ssrc", uint32(parameters.Encodings[idx].SSRC))
+
+			trackEncoding.rtxRtcpInterceptor = r.api.interceptor.BindRTCPReader(
+				interceptor.RTCPReaderFunc(func(in []byte, a interceptor.Attributes) (n int, attributes interceptor.Attributes, err error) {
+					n, err = trackEncoding.rtxSrtpStream.Read(in)
+					return n, a, err
+				}),
+			)
+
+			r.api.interceptor.BindLocalStream(
+				&trackEncoding.rtxStreamInfo,
+				interceptor.RTPWriterFunc(func(header *rtp.Header, payload []byte, attributes interceptor.Attributes) (int, error) {
+					return rtxSrtpStream.WriteRTP(header, payload)
+				}),
+			)
+		}
 	}
 
 	close(r.sendCalled)
@@ -402,6 +447,36 @@ func (r *RTPSender) ReadRTCP() ([]rtcp.Packet, interceptor.Attributes, error) {
 	return pkts, attributes, nil
 }
 
+// ReadRtx reads incoming RTX Stream RTCP for this RTPSender
+func (r *RTPSender) ReadRtx(b []byte) (n int, a interceptor.Attributes, err error) {
+	if r.trackEncodings[0].rtxRtcpInterceptor == nil {
+		return 0, nil, io.ErrNoProgress
+	}
+
+	select {
+	case <-r.sendCalled:
+		return r.trackEncodings[0].rtxRtcpInterceptor.Read(b, a)
+	case <-r.stopCalled:
+		return 0, nil, io.ErrClosedPipe
+	}
+}
+
+// ReadRtxRTCP is a convenience method that wraps ReadRtx and unmarshals for you.
+func (r *RTPSender) ReadRtxRTCP() ([]rtcp.Packet, interceptor.Attributes, error) {
+	b := make([]byte, r.api.settingEngine.getReceiveMTU())
+	i, attributes, err := r.ReadRtx(b)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	pkts, err := rtcp.Unmarshal(b[:i])
+	if err != nil {
+		return nil, nil, err
+	}
+
+	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 {

sdp.go

@@ -389,7 +389,13 @@ func addSenderSDP(
 
 		sendParameters := sender.GetParameters()
 		for _, encoding := range sendParameters.Encodings {
+			if encoding.RTX.SSRC != 0 {
+				media = media.WithValueAttribute(sdp.AttrKeySSRCGroup, fmt.Sprintf("FID %d %d", encoding.SSRC, encoding.RTX.SSRC))
+			}
 			media = media.WithMediaSource(uint32(encoding.SSRC), track.StreamID() /* cname */, track.StreamID() /* streamLabel */, track.ID())
+			if encoding.RTX.SSRC != 0 {
+				media = media.WithMediaSource(uint32(encoding.RTX.SSRC), track.StreamID() /* cname */, track.StreamID() /* streamLabel */, track.ID())
+			}
 			if !isPlanB {
 				media = media.WithPropertyAttribute("msid:" + track.StreamID() + " " + track.ID())
 			}

settingengine.go

@@ -92,6 +92,7 @@ type SettingEngine struct {
 	srtpProtectionProfiles                    []dtls.SRTPProtectionProfile
 	receiveMTU                                uint
 	iceMaxBindingRequests                     *uint16
+	trackLocalRtx                             bool
 }
 
 // getReceiveMTU returns the configured MTU. If SettingEngine's MTU is configured to 0 it returns the default
@@ -437,3 +438,8 @@ func (e *SettingEngine) SetSCTPMaxReceiveBufferSize(maxReceiveBufferSize uint32)
 func (e *SettingEngine) SetDTLSCustomerCipherSuites(customCipherSuites func() []dtls.CipherSuite) {
 	e.dtls.customCipherSuites = customCipherSuites
 }
+
+// SetTrackLocalRtx allows track local use RTX.
+func (e *SettingEngine) SetTrackLocalRtx(enable bool) {
+	e.trackLocalRtx = enable
+}

track_local.go

@@ -44,8 +44,9 @@ type TrackLocalContext interface {
 }
 
 type baseTrackLocalContext struct {
-	id              string
-	params          RTPParameters
+	id     string
+	params RTPParameters
+
 	ssrc            SSRC
 	writeStream     TrackLocalWriter
 	rtcpInterceptor interceptor.RTCPReader