Track的添加

上图是整体流程图 

RTCErrorOr<rtc::scoped_refptr<RtpSenderInterface>> PeerConnection::AddTrack(rtc::scoped_refptr<MediaStreamTrackInterface> track,const std::vector<std::string>& stream_ids) {RTC_DCHECK_RUN_ON(signaling_thread());TRACE_EVENT0("webrtc", "PeerConnection::AddTrack");if (!track) {LOG_AND_RETURN_ERROR(RTCErrorType::INVALID_PARAMETER, "Track is null.");}//如果不是音频或者视频轨就返回if (!(track->kind() == MediaStreamTrackInterface::kAudioKind ||track->kind() == MediaStreamTrackInterface::kVideoKind)) {LOG_AND_RETURN_ERROR(RTCErrorType::INVALID_PARAMETER,"Track has invalid kind: " + track->kind());}//判断PC是否关闭if (IsClosed()) {LOG_AND_RETURN_ERROR(RTCErrorType::INVALID_STATE,