Method setCodecPreferencesFromRemoteDescription

rtptransceiver.go:97–183

match codecs from remote description, used when remote is offerer and creating a transceiver from remote description with the aim of keeping order of codecs in remote description.

(media *sdp.MediaDescription)

// match codecs from remote description, used when remote is offerer and creating a transceiver
// from remote description with the aim of keeping order of codecs in remote description.
func (t *RTPTransceiver) setCodecPreferencesFromRemoteDescription(media *sdp.MediaDescription) { //nolint:cyclop
	remoteCodecs, err := codecsFromMediaDescription(media)
	if err != nil {
		return
	}

	// make a copy as this slice is modified
	leftCodecs := append([]RTPCodecParameters{}, t.api.mediaEngine.getCodecsByKind(t.kind)...)

	// find codec matches between what is in remote description and
	// the transceivers codecs and use payload type registered to
	// media engine.
	payloadMapping := make(map[PayloadType]PayloadType) // for RTX re-mapping later
	filterByMatchType := func(matchFilter codecMatchType) []RTPCodecParameters {
		filteredCodecs := []RTPCodecParameters{}
		for remoteCodecIdx := len(remoteCodecs) - 1; remoteCodecIdx >= 0; remoteCodecIdx-- {
			remoteCodec := remoteCodecs[remoteCodecIdx]
			if strings.EqualFold(remoteCodec.RTPCodecCapability.MimeType, MimeTypeRTX) {
				continue
			}

			matchCodec, matchType := codecParametersFuzzySearch(
				remoteCodec,
				leftCodecs,
			)
			if matchType == matchFilter {
				payloadMapping[remoteCodec.PayloadType] = matchCodec.PayloadType

				remoteCodec.PayloadType = matchCodec.PayloadType
				filteredCodecs = append([]RTPCodecParameters{remoteCodec}, filteredCodecs...)

				// removed matched codec for next round
				remoteCodecs = append(remoteCodecs[:remoteCodecIdx], remoteCodecs[remoteCodecIdx+1:]...)

				needleFmtp := fmtp.Parse(
					matchCodec.RTPCodecCapability.MimeType,
					matchCodec.RTPCodecCapability.ClockRate,
					matchCodec.RTPCodecCapability.Channels,
					matchCodec.RTPCodecCapability.SDPFmtpLine,
				)

				for leftCodecIdx := len(leftCodecs) - 1; leftCodecIdx >= 0; leftCodecIdx-- {
					leftCodec := leftCodecs[leftCodecIdx]
					leftCodecFmtp := fmtp.Parse(
						leftCodec.RTPCodecCapability.MimeType,
						leftCodec.RTPCodecCapability.ClockRate,
						leftCodec.RTPCodecCapability.Channels,
						leftCodec.RTPCodecCapability.SDPFmtpLine,
					)

					if needleFmtp.Match(leftCodecFmtp) {
						leftCodecs = append(leftCodecs[:leftCodecIdx], leftCodecs[leftCodecIdx+1:]...)

						break
					}
				}
			}
		}