Fix missing RTX codec using SetCodecPreferences

Author: stephanrotolante

rtpcodec.go

@@ -143,7 +143,7 @@ func codecParametersFuzzySearch(
 	return RTPCodecParameters{}, codecMatchNone
 }
 
-// Given a CodecParameters find the RTX CodecParameters if one exists.
+// Given a CodecParameters find the RTX Payload if one exists.
 func findRTXPayloadType(needle PayloadType, haystack []RTPCodecParameters) PayloadType {
 	aptStr := fmt.Sprintf("apt=%d", needle)
 	for _, c := range haystack {
@@ -155,6 +155,29 @@ func findRTXPayloadType(needle PayloadType, haystack []RTPCodecParameters) Paylo
 	return PayloadType(0)
 }
 
+// Given a RTPCodecParameters check if it exists in a of other RTPCodecParameters.
+func doesCodecExistInList(codec RTPCodecParameters, codecList []RTPCodecParameters) bool {
+	for _, c := range codecList {
+		if codec.SDPFmtpLine == c.SDPFmtpLine && codec.MimeType == c.MimeType {
+			return true
+		}
+	}
+
+	return false
+}
+
+// Given a CodecParameters find the RTX CodecParameters if one exists.
+func findRTXPCodec(needle PayloadType, haystack []RTPCodecParameters) *RTPCodecParameters {
+	aptStr := fmt.Sprintf("apt=%d", needle)
+	for _, c := range haystack {
+		if aptStr == c.SDPFmtpLine {
+			return &c
+		}
+	}
+
+	return nil
+}
+
 func rtcpFeedbackIntersection(a, b []RTCPFeedback) (out []RTCPFeedback) {
 	for _, aFeedback := range a {
 		for _, bFeeback := range b {

rtptransceiver.go

@@ -86,6 +86,17 @@ func (t *RTPTransceiver) getCodecs() []RTPCodecParameters {
 		}
 	}
 
+	// check if direction is specified
+	if t.direction.Load() != nil {
+		for _, c := range filteredCodecs {
+			if rtxCodec := findRTXPCodec(c.PayloadType, mediaEngineCodecs); rtxCodec != nil {
+				if !doesCodecExistInList(*rtxCodec, filteredCodecs) {
+					filteredCodecs = append(filteredCodecs, *rtxCodec)
+				}
+			}
+		}
+	}
+
 	return filteredCodecs
 }
 

rtptransceiver_test.go

@@ -135,3 +135,53 @@ func Test_RTPTransceiver_SetCodecPreferences_PayloadType(t *testing.T) {
 
 	closePairNow(t, offerPC, answerPC)
 }
+
+// func Test_RTPTransceiver_SDP_Codec(t *testing.T) {
+// 	tests := []struct {
+// 		Label          string
+// 		setPreferences bool
+// 	}{
+// 		{
+// 			Label:          "NoSetCodecPreferences",
+// 			setPreferences: false,
+// 		},
+// 		{
+// 			Label:          "SetCodecPreferences",
+// 			setPreferences: true,
+// 		},
+// 	}
+
+// 	for _, test := range tests {
+// 		t.Run(test.Label, func(t *testing.T) {
+// 			pc, err := NewPeerConnection(Configuration{})
+// 			assert.NoError(t, err)
+
+// 			transceiver, err := pc.AddTransceiverFromKind(
+// 				RTPCodecTypeVideo,
+// 				RTPTransceiverInit{
+// 					Direction: RTPTransceiverDirectionRecvonly,
+// 				},
+// 			)
+// 			assert.NoError(t, err)
+
+// 			if test.setPreferences {
+// 				codec := RTPCodecCapability{
+// 					"video/vp8", 90000, 0, "", nil,
+// 				}
+
+// 				assert.NoError(t, transceiver.SetCodecPreferences(
+// 					[]RTPCodecParameters{
+// 						{
+// 							RTPCodecCapability: codec,
+// 						},
+// 					},
+// 				))
+// 			}
+
+// 			offer, err := pc.CreateOffer(nil)
+// 			assert.NoError(t, err)
+
+// 			assert.Equal(t, true, strings.Contains(offer.SDP, "apt=96"))
+// 		})
+// 	}
+// }