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 +155,46 @@ func findRTXPayloadType(needle PayloadType, haystack []RTPCodecParameters) Paylo
 	return PayloadType(0)
 }
 
+// Given a RTPCodecParameters check if it exists in a list of other RTPCodecParameters.
+func doesCodecExistInList(
+	needle RTPCodecParameters,
+	haystack []RTPCodecParameters,
+) bool {
+	needleFmtp := fmtp.Parse(
+		needle.RTPCodecCapability.MimeType,
+		needle.RTPCodecCapability.ClockRate,
+		needle.RTPCodecCapability.Channels,
+		needle.RTPCodecCapability.SDPFmtpLine,
+	)
+
+	for _, c := range haystack {
+		cfmtp := fmtp.Parse(
+			c.RTPCodecCapability.MimeType,
+			c.RTPCodecCapability.ClockRate,
+			c.RTPCodecCapability.Channels,
+			c.RTPCodecCapability.SDPFmtpLine,
+		)
+
+		if needleFmtp.Match(cfmtp) {
+			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 {

rtpcodec_test.go

@@ -0,0 +1,58 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+//go:build !js
+// +build !js
+
+package webrtc
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_DoesCodecExistInList(t *testing.T) {
+	mediaEngine := &MediaEngine{}
+	NewAPI(WithMediaEngine(mediaEngine))
+	assert.NoError(t, mediaEngine.RegisterDefaultCodecs())
+
+	codecs := mediaEngine.getCodecsByKind(RTPCodecTypeVideo)
+
+	tests := []struct {
+		Label  string
+		Result bool
+		Codec  RTPCodecParameters
+	}{
+		{
+			Label:  "Codec does not exist in list",
+			Result: false,
+			Codec: RTPCodecParameters{
+				RTPCodecCapability: RTPCodecCapability{
+					"I am bad mimetype",
+					90000,
+					0,
+					"",
+					[]RTCPFeedback{
+						{"goog-remb", ""},
+						{"ccm", "fir"},
+						{"nack", ""},
+						{"nack", "pli"},
+					},
+				},
+				PayloadType: 96,
+			},
+		},
+		{
+			Label:  "Codec does exist in list",
+			Result: true,
+			Codec:  codecs[0],
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.Label, func(t *testing.T) {
+			assert.Equal(t, test.Result, doesCodecExistInList(test.Codec, codecs))
+		})
+	}
+}

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 +135,55 @@ 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,
+				}
+
+				err = transceiver.SetCodecPreferences(
+					[]RTPCodecParameters{
+						{
+							RTPCodecCapability: codec,
+						},
+					},
+				)
+				assert.NoError(t, err)
+			}
+
+			offer, err := pc.CreateOffer(nil)
+			assert.NoError(t, err)
+
+			assert.Equal(t, true, strings.Contains(offer.SDP, "apt=96"))
+			assert.NoError(t, pc.Close())
+		})
+	}
+}