Fixes MediaEngine: codec apt negotiation

codec has apt fmtp can't negotiation because it's
apt payloadtype can't be found in negotiation codecs.
rtx codec must be partial match if apt codec is partial.

Was reverted in eeb67e1

Fixes pion#1785

mediaengine.go

@@ -334,7 +334,7 @@ func (m *MediaEngine) collectStats(collector *statsReportCollector) {
 }
 
 // Look up a codec and enable if it exists
-func (m *MediaEngine) matchRemoteCodec(remoteCodec RTPCodecParameters, typ RTPCodecType) (codecMatchType, error) {
+func (m *MediaEngine) matchRemoteCodec(remoteCodec RTPCodecParameters, typ RTPCodecType, exactMatches, partialMatches []RTPCodecParameters) (codecMatchType, error) {
 	codecs := m.videoCodecs
 	if typ == RTPCodecTypeAudio {
 		codecs = m.audioCodecs
@@ -347,9 +347,33 @@ func (m *MediaEngine) matchRemoteCodec(remoteCodec RTPCodecParameters, typ RTPCo
 			return codecMatchNone, err
 		}
 
-		if _, _, err = m.getCodecByPayload(PayloadType(payloadType)); err != nil {
+		aptMatch := codecMatchNone
+		for _, codec := range exactMatches {
+			if codec.PayloadType == PayloadType(payloadType) {
+				aptMatch = codecMatchExact
+				break
+			}
+		}
+
+		if aptMatch == codecMatchNone {
+			for _, codec := range partialMatches {
+				if codec.PayloadType == PayloadType(payloadType) {
+					aptMatch = codecMatchPartial
+					break
+				}
+			}
+		}
+
+		if aptMatch == codecMatchNone {
 			return codecMatchNone, nil // not an error, we just ignore this codec we don't support
 		}
+
+		// if apt's media codec is partial match, then apt codec must be partial match too
+		_, matchType := codecParametersFuzzySearch(remoteCodec, codecs)
+		if matchType == codecMatchExact && aptMatch == codecMatchPartial {
+			matchType = codecMatchPartial
+		}
+		return matchType, nil
 	}
 
 	_, matchType := codecParametersFuzzySearch(remoteCodec, codecs)
@@ -416,7 +440,7 @@ func (m *MediaEngine) updateFromRemoteDescription(desc sdp.SessionDescription) e
 		partialMatches := make([]RTPCodecParameters, 0, len(codecs))
 
 		for _, codec := range codecs {
-			matchType, mErr := m.matchRemoteCodec(codec, typ)
+			matchType, mErr := m.matchRemoteCodec(codec, typ, exactMatches, partialMatches)
 			if mErr != nil {
 				return mErr
 			}

mediaengine_test.go

@@ -280,6 +280,72 @@ a=rtpmap:96 VP8/90000
 		_, _, err := m.getCodecByPayload(96)
 		assert.NoError(t, err)
 	})
+
+	t.Run("Matches when rtx apt for exact match codec", func(t *testing.T) {
+		const profileLevels = `v=0
+o=- 4596489990601351948 2 IN IP4 127.0.0.1
+s=-
+t=0 0
+m=video 60323 UDP/TLS/RTP/SAVPF 94 96 97
+a=rtpmap:94 VP8/90000
+a=rtpmap:96 VP9/90000
+a=fmtp:96 profile-id=2
+a=rtpmap:97 rtx/90000
+a=fmtp:97 apt=96
+`
+		m := MediaEngine{}
+		assert.NoError(t, m.RegisterCodec(RTPCodecParameters{
+			RTPCodecCapability: RTPCodecCapability{MimeTypeVP8, 90000, 0, "", nil},
+			PayloadType:        94,
+		}, RTPCodecTypeVideo))
+		assert.NoError(t, m.RegisterCodec(RTPCodecParameters{
+			RTPCodecCapability: RTPCodecCapability{MimeTypeVP9, 90000, 0, "profile-id=2", nil},
+			PayloadType:        96,
+		}, RTPCodecTypeVideo))
+		assert.NoError(t, m.RegisterCodec(RTPCodecParameters{
+			RTPCodecCapability: RTPCodecCapability{"video/rtx", 90000, 0, "apt=96", nil},
+			PayloadType:        97,
+		}, RTPCodecTypeVideo))
+		assert.NoError(t, m.updateFromRemoteDescription(mustParse(profileLevels)))
+
+		assert.True(t, m.negotiatedVideo)
+
+		_, _, err := m.getCodecByPayload(97)
+		assert.NoError(t, err)
+	})
+
+	t.Run("Matches when rtx apt for partial match codec", func(t *testing.T) {
+		const profileLevels = `v=0
+o=- 4596489990601351948 2 IN IP4 127.0.0.1
+s=-
+t=0 0
+m=video 60323 UDP/TLS/RTP/SAVPF 94 96 97
+a=rtpmap:94 VP8/90000
+a=rtpmap:96 VP9/90000
+a=fmtp:96 profile-id=2
+a=rtpmap:97 rtx/90000
+a=fmtp:97 apt=96
+`
+		m := MediaEngine{}
+		assert.NoError(t, m.RegisterCodec(RTPCodecParameters{
+			RTPCodecCapability: RTPCodecCapability{MimeTypeVP8, 90000, 0, "", nil},
+			PayloadType:        94,
+		}, RTPCodecTypeVideo))
+		assert.NoError(t, m.RegisterCodec(RTPCodecParameters{
+			RTPCodecCapability: RTPCodecCapability{MimeTypeVP9, 90000, 0, "profile-id=1", nil},
+			PayloadType:        96,
+		}, RTPCodecTypeVideo))
+		assert.NoError(t, m.RegisterCodec(RTPCodecParameters{
+			RTPCodecCapability: RTPCodecCapability{"video/rtx", 90000, 0, "apt=96", nil},
+			PayloadType:        97,
+		}, RTPCodecTypeVideo))
+		assert.NoError(t, m.updateFromRemoteDescription(mustParse(profileLevels)))
+
+		assert.True(t, m.negotiatedVideo)
+
+		_, _, err := m.getCodecByPayload(97)
+		assert.ErrorIs(t, err, ErrCodecNotFound)
+	})
 }
 
 func TestMediaEngineHeaderExtensionDirection(t *testing.T) {