這里看下視頻發送和接收處理過程。分析所基于的應用程序，依然選擇 WebRTC 的示例應用 peerconnection_client，代碼版本 M96。

應用層創建 VideoTrackSource，創建 VideoTrackInterface，啟動本地渲染，并將 VideoTrack 添加進 PeerConnection 中:

void Conductor::AddTracks() {if (!peer_connection_->GetSenders().empty()) {return; // Already added tracks.} . . . . . .rtc::scoped_refptr<CapturerTrackSource> video_device =CapturerTrackSource::Create();if (video_device) {rtc::scoped_refptr<webrtc::VideoTrackInterface> video_track_(peer_connection_factory_->CreateVideoTrack(kVideoLabel, video_device));main_wnd_->StartLocalRenderer(video_track_);result_or_error = peer_connection_->AddTrack(video_track_, {kStreamId});if (!result_or_error.ok()) {RTC_LOG(LS_ERROR) << "Failed to add video track to PeerConnection: "<< result_or_error.error().message();}} else {RTC_LOG(LS_ERROR) << "OpenVideoCaptureDevice failed";}main_wnd_->SwitchToStreamingUI(); }

在創建 VideoTrackSource，也就是 CapturerTrackSource 時，就會啟動攝像頭捕捉畫面 StartCapture()：

#0 webrtc::videocapturemodule::VideoCaptureModuleV4L2::StartCapture(webrtc::VideoCaptureCapability const&)(this=0x5555557d13b9 <webrtc::MutexImpl::OwnerRecord::SetOwner()+21>, capability=...) at ../../modules/video_capture/linux/video_capture_linux.cc:106 #1 0x00005555557bc2fb in webrtc::test::VcmCapturer::Init(unsigned long, unsigned long, unsigned long, unsigned long)(this=0x555558953630, width=640, height=480, target_fps=30, capture_device_index=0) at ../../test/vcm_capturer.cc:55 #2 0x00005555557bc480 in webrtc::test::VcmCapturer::Create(unsigned long, unsigned long, unsigned long, unsigned long)(width=640, height=480, target_fps=30, capture_device_index=0) at ../../test/vcm_capturer.cc:70 #3 0x000055555579f35c in (anonymous namespace)::CapturerTrackSource::Create() () at ../../examples/peerconnection/client/conductor.cc:85 #4 0x00005555557a4545 in Conductor::AddTracks() (this=0x555558625bc0) at ../../examples/peerconnection/client/conductor.cc:454 #5 0x000055555579fb87 in Conductor::InitializePeerConnection() (this=0x555558625bc0) at ../../examples/peerconnection/client/conductor.cc:158

VideoCaptureModuleV4L2 內部會起一個視頻捕捉線程，捕捉視頻幀并把視頻幀吐出去：

#6 0x0000555555907c22 in webrtc::videocapturemodule::VideoCaptureModuleV4L2::CaptureProcess() (this=0x555558685130)at ../../modules/video_capture/linux/video_capture_linux.cc:411 #7 0x0000555555904f93 in webrtc::videocapturemodule::VideoCaptureModuleV4L2::<lambda()>::operator()(void) const (__closure=0x555558475490)at ../../modules/video_capture/linux/video_capture_linux.cc:247 #8 0x0000555555907f55 in std::_Function_handler<void(), webrtc::videocapturemodule::VideoCaptureModuleV4L2::StartCapture(const webrtc::VideoCaptureCapability&)::<lambda()> >::_M_invoke(const std::_Any_data &) (__functor=...) at /usr/include/c++/9/bits/std_function.h:300

CapturerTrackSource（VcmCapturer/VideoCaptureModuleV4L2）可以從硬件設備獲取視頻幀并吐出去。啟動本地渲染的時候，會向 CapturerTrackSource 注冊一個渲染器 (webrtc/src/examples/peerconnection/client/linux/main_wnd.cc)：

void GtkMainWnd::StartLocalRenderer(webrtc::VideoTrackInterface* local_video) {local_renderer_.reset(new VideoRenderer(this, local_video)); }void GtkMainWnd::StopLocalRenderer() {local_renderer_.reset(); } . . . . . . GtkMainWnd::VideoRenderer::VideoRenderer(GtkMainWnd* main_wnd,webrtc::VideoTrackInterface* track_to_render): width_(0),height_(0),main_wnd_(main_wnd),rendered_track_(track_to_render) {rendered_track_->AddOrUpdateSink(this, rtc::VideoSinkWants()); }GtkMainWnd::VideoRenderer::~VideoRenderer() {rendered_track_->RemoveSink(this); }

視頻渲染器將視頻捕捉模塊和圖形渲染模塊連接起來。它從視頻捕捉模塊收取視頻幀，然后通過系統的窗口系統提供的圖形渲染接口將視頻幀渲染出來。視頻渲染器收到視頻捕捉模塊送過來視頻幀的過程如下：

#0 GtkMainWnd::VideoRenderer::OnFrame(webrtc::VideoFrame const&) (this=0x5555589536a0, video_frame=...)at ../../examples/peerconnection/client/linux/main_wnd.cc:548 #1 0x0000555556037b5f in rtc::VideoBroadcaster::OnFrame(webrtc::VideoFrame const&) (this=0x555558953678, frame=...)at ../../media/base/video_broadcaster.cc:90 #2 0x00005555557ddd6c in webrtc::test::TestVideoCapturer::OnFrame(webrtc::VideoFrame const&) (this=0x555558953630, original_frame=...)at ../../test/test_video_capturer.cc:62 #3 0x00005555557bcc17 in webrtc::test::VcmCapturer::OnFrame(webrtc::VideoFrame const&) (this=0x555558953630, frame=...) at ../../test/vcm_capturer.cc:94 #4 0x000055555614d6cd in webrtc::videocapturemodule::VideoCaptureImpl::DeliverCapturedFrame(webrtc::VideoFrame&) (this=0x5555584ba400, captureFrame=...)at ../../modules/video_capture/video_capture_impl.cc:111 #5 0x000055555614e05a in webrtc::videocapturemodule::VideoCaptureImpl::IncomingFrame(unsigned char*, unsigned long, webrtc::VideoCaptureCapability const&, long)(this=0x5555584ba400, videoFrame=0x7fffcdd32000 "\022\177"..., videoFrameLength=614400, frameInfo=..., captureTime=0) at ../../modules/video_capture/video_capture_impl.cc:201 #6 0x0000555555907c22 in webrtc::videocapturemodule::VideoCaptureModuleV4L2::CaptureProcess() (this=0x5555584ba400)

實際的渲染過程還要稍微復雜一點。渲染器收到視頻幀之后，先將視頻幀的格式做一些轉換，如將 YUV 轉成 ARGB，旋轉等，然后調度窗口系統取渲染：

void GtkMainWnd::VideoRenderer::OnFrame(const webrtc::VideoFrame& video_frame) {gdk_threads_enter();rtc::scoped_refptr<webrtc::I420BufferInterface> buffer(video_frame.video_frame_buffer()->ToI420());if (video_frame.rotation() != webrtc::kVideoRotation_0) {buffer = webrtc::I420Buffer::Rotate(*buffer, video_frame.rotation());}SetSize(buffer->width(), buffer->height());// TODO(bugs.webrtc.org/6857): This conversion is correct for little-endian// only. Cairo ARGB32 treats pixels as 32-bit values in *native* byte order,// with B in the least significant byte of the 32-bit value. Which on// little-endian means that memory layout is BGRA, with the B byte stored at// lowest address. Libyuv's ARGB format (surprisingly?) uses the same// little-endian format, with B in the first byte in memory, regardless of// native endianness.libyuv::I420ToARGB(buffer->DataY(), buffer->StrideY(), buffer->DataU(),buffer->StrideU(), buffer->DataV(), buffer->StrideV(),image_.get(), width_ * 4, buffer->width(),buffer->height());gdk_threads_leave();g_idle_add(Redraw, main_wnd_); }

接上面看到的函數中最后一行調度的 Redraw() 函數，更詳細的渲染過程如下：

gboolean Redraw(gpointer data) {GtkMainWnd* wnd = reinterpret_cast<GtkMainWnd*>(data);wnd->OnRedraw();return false; } . . . . . . void GtkMainWnd::OnRedraw() {gdk_threads_enter();VideoRenderer* remote_renderer = remote_renderer_.get();if (remote_renderer && remote_renderer->image() != NULL &&draw_area_ != NULL) {width_ = remote_renderer->width();height_ = remote_renderer->height();if (!draw_buffer_.get()) {draw_buffer_size_ = (width_ * height_ * 4) * 4;draw_buffer_.reset(new uint8_t[draw_buffer_size_]);gtk_widget_set_size_request(draw_area_, width_ * 2, height_ * 2);}const uint32_t* image =reinterpret_cast<const uint32_t*>(remote_renderer->image());uint32_t* scaled = reinterpret_cast<uint32_t*>(draw_buffer_.get());for (int r = 0; r < height_; ++r) {for (int c = 0; c < width_; ++c) {int x = c * 2;scaled[x] = scaled[x + 1] = image[c];}uint32_t* prev_line = scaled;scaled += width_ * 2;memcpy(scaled, prev_line, (width_ * 2) * 4);image += width_;scaled += width_ * 2;}VideoRenderer* local_renderer = local_renderer_.get();if (local_renderer && local_renderer->image()) {image = reinterpret_cast<const uint32_t*>(local_renderer->image());scaled = reinterpret_cast<uint32_t*>(draw_buffer_.get());// Position the local preview on the right side.scaled += (width_ * 2) - (local_renderer->width() / 2);// right margin...scaled -= 10;// ... towards the bottom.scaled += (height_ * width_ * 4) - ((local_renderer->height() / 2) *(local_renderer->width() / 2) * 4);// bottom margin...scaled -= (width_ * 2) * 5;for (int r = 0; r < local_renderer->height(); r += 2) {for (int c = 0; c < local_renderer->width(); c += 2) {scaled[c / 2] = image[c + r * local_renderer->width()];}scaled += width_ * 2;}}#if GTK_MAJOR_VERSION == 2gdk_draw_rgb_32_image(draw_area_->window,draw_area_->style->fg_gc[GTK_STATE_NORMAL], 0, 0,width_ * 2, height_ * 2, GDK_RGB_DITHER_MAX,draw_buffer_.get(), (width_ * 2) * 4); #elsegtk_widget_queue_draw(draw_area_); #endif}gdk_threads_leave(); }

如上面這段代碼，peerconnection_client 的實現中，當遠端渲染器存在時，才會真正開始渲染，包括本地預覽和遠端畫面 —— 本地預覽是畫在遠端畫面的大窗口中的一小塊區域上的。

VideoCaptureModuleV4L2 視頻捕捉模塊在將捕捉的視頻幀送進渲染器去做本地預覽之外，還會將視頻幀送進視頻編碼器里：

#0 webrtc::VideoStreamEncoder::OnFrame(webrtc::VideoFrame const&) (this=0xf0000000a0, video_frame=...) at ../../video/video_stream_encoder.cc:1264 #1 0x0000555556037b5f in rtc::VideoBroadcaster::OnFrame(webrtc::VideoFrame const&) (this=0x5555586e1678, frame=...)at ../../media/base/video_broadcaster.cc:90 #2 0x00005555557ddd20 in webrtc::test::TestVideoCapturer::OnFrame(webrtc::VideoFrame const&) (this=0x5555586e1630, original_frame=...)at ../../test/test_video_capturer.cc:58 #3 0x00005555557bcc17 in webrtc::test::VcmCapturer::OnFrame(webrtc::VideoFrame const&) (this=0x5555586e1630, frame=...) at ../../test/vcm_capturer.cc:94 #4 0x000055555614d6cd in webrtc::videocapturemodule::VideoCaptureImpl::DeliverCapturedFrame(webrtc::VideoFrame&) (this=0x5555587da600, captureFrame=...)at ../../modules/video_capture/video_capture_impl.cc:111 #5 0x000055555614e05a in webrtc::videocapturemodule::VideoCaptureImpl::IncomingFrame(unsigned char*, unsigned long, webrtc::VideoCaptureCapability const&, long)(this=0x5555587da600, videoFrame=0x7fffd9d32000 "\022\177"..., videoFrameLength=614400, frameInfo=..., captureTime=0) at ../../modules/video_capture/video_capture_impl.cc:201 #6 0x0000555555907c22 in webrtc::videocapturemodule::VideoCaptureModuleV4L2::CaptureProcess() (this=0x5555587da600)at ../../modules/video_capture/linux/video_capture_linux.cc:411

視頻編碼器在視頻幀編碼結束后，將編碼的視頻幀送進 PacedSender 的隊列里：

#0 webrtc::PacingController::EnqueuePacket(std::unique_ptr<webrtc::RtpPacketToSend, std::default_delete<webrtc::RtpPacketToSend> >)(this=0x55555692fb9a <std::tuple<webrtc::RtpPacketToSend*, std::default_delete<webrtc::RtpPacketToSend> >::tuple<webrtc::RtpPacketToSend*&, std::default_delete<webrtc::RtpPacketToSend>, true>(webrtc::RtpPacketToSend*&, std::default_delete<webrtc::RtpPacketToSend>&&)+72>, packet=std::unique_ptr<webrtc::RtpPacketToSend> = {...}) at ../../modules/pacing/pacing_controller.cc:235 #1 0x000055555692edbc in webrtc::PacedSender::EnqueuePackets(std::vector<std::unique_ptr<webrtc::RtpPacketToSend, std::default_delete<webrtc::RtpPacketToSend> >, std::allocator<std::unique_ptr<webrtc::RtpPacketToSend, std::default_delete<webrtc::RtpPacketToSend> > > >)(this=0x7fffc408e530, packets=std::vector of length 3, capacity 4 = {...}) at ../../modules/pacing/paced_sender.cc:128 #2 0x0000555557425593 in webrtc::RTPSender::EnqueuePackets(std::vector<std::unique_ptr<webrtc::RtpPacketToSend, std::default_delete<webrtc::RtpPacketToSend> >, std::allocator<std::unique_ptr<webrtc::RtpPacketToSend, std::default_delete<webrtc::RtpPacketToSend> > > >)(this=0x7fffc405f4c0, packets=std::vector of length 0, capacity 0) at ../../modules/rtp_rtcp/source/rtp_sender.cc:517 #3 0x000055555743750f in webrtc::RTPSenderVideo::LogAndSendToNetwork(std::vector<std::unique_ptr<webrtc::RtpPacketToSend, std::default_delete<webrtc::RtpPacketToSend> >, std::allocator<std::unique_ptr<webrtc::RtpPacketToSend, std::default_delete<webrtc::RtpPacketToSend> > > >, unsigned long)(this=0x7fffc40602c0, packets=std::vector of length 0, capacity 0, unpacketized_payload_size=2711)at ../../modules/rtp_rtcp/source/rtp_sender_video.cc:210 #4 0x000055555743b701 in webrtc::RTPSenderVideo::SendVideo(int, absl::optional<webrtc::VideoCodecType>, unsigned int, long, rtc::ArrayView<unsigned char const, -4711l>, webrtc::RTPVideoHeader, absl::optional<long>, absl::optional<long>)(this=0x7fffc40602c0, payload_type=96, codec_type=..., rtp_timestamp=182197814, capture_time_ms=50000169, payload=..., video_header=..., expected_retransmission_time_ms=..., estimated_capture_clock_offset_ms=...) at ../../modules/rtp_rtcp/source/rtp_sender_video.cc:711 #5 0x000055555743bb06 in webrtc::RTPSenderVideo::SendEncodedImage(int, absl::optional<webrtc::VideoCodecType>, unsigned int, webrtc::EncodedImage const&, webrtc::RTPVideoHeader, absl::optional<long>)(this=0x7fffc40602c0, payload_type=96, codec_type=..., rtp_timestamp=182197814, encoded_image=..., video_header=..., expected_retransmission_time_ms=...)at ../../modules/rtp_rtcp/source/rtp_sender_video.cc:750 #6 0x00005555568ec887 in webrtc::RtpVideoSender::OnEncodedImage(webrtc::EncodedImage const&, webrtc::CodecSpecificInfo const*)(this=0x7fffc40a95a0, encoded_image=..., codec_specific_info=0x7fffd8d64950) at ../../call/rtp_video_sender.cc:604 #7 0x0000555556a612e2 in webrtc::internal::VideoSendStreamImpl::OnEncodedImage(webrtc::EncodedImage const&, webrtc::CodecSpecificInfo const*)(this=0x7fffc40a31b0, encoded_image=..., codec_specific_info=0x7fffd8d64950) at ../../video/video_send_stream_impl.cc:566 #8 0x0000555556adbc25 in webrtc::VideoStreamEncoder::OnEncodedImage(webrtc::EncodedImage const&, webrtc::CodecSpecificInfo const*) (this=0x7fffc40a4c90, encoded_image=..., codec_specific_info=0x7fffd8d64950) at ../../video/video_stream_encoder.cc:1936 #9 0x0000555557553770 in webrtc::LibvpxVp8Encoder::GetEncodedPartitions(webrtc::VideoFrame const&, bool) (this=0x7fff880022f0, input_image=..., retransmission_allowed=true) at ../../modules/video_coding/codecs/vp8/libvpx_vp8_encoder.cc:1188 #10 0x0000555557552801 in webrtc::LibvpxVp8Encoder::Encode(webrtc::VideoFrame const&, std::vector<webrtc::VideoFrameType, std::allocator<webrtc::VideoFrameType> > const*) (this=0x7fff880022f0, frame=..., frame_types=0x7fffc40a54d0) at ../../modules/video_coding/codecs/vp8/libvpx_vp8_encoder.cc:1075 #11 0x0000555556f92ad5 in webrtc::EncoderSimulcastProxy::Encode(webrtc::VideoFrame const&, std::vector<webrtc::VideoFrameType, std::allocator<webrtc::VideoFrameType> > const*) (this=0x7fff88002270, input_image=..., frame_types=0x7fffc40a54d0) at ../../media/engine/encoder_simulcast_proxy.cc:53 #12 0x0000555556ada0c0 in webrtc::VideoStreamEncoder::EncodeVideoFrame(webrtc::VideoFrame const&, long)(this=0x7fffc40a4c90, video_frame=..., time_when_posted_us=50000169389) at ../../video/video_stream_encoder.cc:1767 #13 0x0000555556ad8426 in webrtc::VideoStreamEncoder::MaybeEncodeVideoFrame(webrtc::VideoFrame const&, long)(this=0x7fffc40a4c90, video_frame=..., time_when_posted_us=50000169389) at ../../video/video_stream_encoder.cc:1636 #14 0x0000555556ad3da1 in webrtc::VideoStreamEncoder::<lambda()>::operator()(void) const (__closure=0x7fffe4002638)at ../../video/video_stream_encoder.cc:1333 #15 0x0000555556aed256 in webrtc::webrtc_new_closure_impl::ClosureTask<webrtc::VideoStreamEncoder::OnFrame(const webrtc::VideoFrame&)::<lambda()> >::Run(void)(this=0x7fffe4002630) at ../../rtc_base/task_utils/to_queued_task.h:32

PacedSender 將 RTP 包通過 MediaChannel 發送出去：

#0 cricket::MediaChannel::SendRtp(unsigned char const*, unsigned long, webrtc::PacketOptions const&)(this=0x7fff9c001398, data=0x69800000005 <error: Cannot access memory at address 0x69800000005>, len=93825004092765, options=...)at ../../media/base/media_channel.cc:169 #1 0x000055555608ce42 in cricket::WebRtcVideoChannel::SendRtp(unsigned char const*, unsigned long, webrtc::PacketOptions const&)(this=0x7fffc4092aa0, data=0x7fffa40017a0 "\260a\002\264", len=248, options=...) at ../../media/engine/webrtc_video_engine.cc:2034 #2 0x0000555557430fd4 in webrtc::RtpSenderEgress::SendPacketToNetwork(webrtc::RtpPacketToSend const&, webrtc::PacketOptions const&, webrtc::PacedPacketInfo const&) (this=0x7fffc405f200, packet=..., options=..., pacing_info=...) at ../../modules/rtp_rtcp/source/rtp_sender_egress.cc:555 #3 0x000055555742e285 in webrtc::RtpSenderEgress::SendPacket(webrtc::RtpPacketToSend*, webrtc::PacedPacketInfo const&)(this=0x7fffc405f200, packet=0x7fff9c001340, pacing_info=...) at ../../modules/rtp_rtcp/source/rtp_sender_egress.cc:273 #4 0x000055555741cc89 in webrtc::ModuleRtpRtcpImpl2::TrySendPacket(webrtc::RtpPacketToSend*, webrtc::PacedPacketInfo const&)(this=0x7fffc405e9f0, packet=0x7fff9c001340, pacing_info=...) at ../../modules/rtp_rtcp/source/rtp_rtcp_impl2.cc:376 #5 0x0000555556936fd5 in webrtc::PacketRouter::SendPacket(std::unique_ptr<webrtc::RtpPacketToSend, std::default_delete<webrtc::RtpPacketToSend> >, webrtc::PacedPacketInfo const&) (this=0x7fffc408df18, packet=std::unique_ptr<webrtc::RtpPacketToSend> = {...}, cluster_info=...)at ../../modules/pacing/packet_router.cc:160 #6 0x00005555569347ca in webrtc::PacingController::ProcessPackets() (this=0x7fffc408e598) at ../../modules/pacing/pacing_controller.cc:590 #7 0x000055555692f1e3 in webrtc::PacedSender::Process() (this=0x7fffc408e530) at ../../modules/pacing/paced_sender.cc:183 #8 0x000055555692f6cb in webrtc::PacedSender::ModuleProxy::Process() (this=0x7fffc408e548) at ../../modules/pacing/paced_sender.h:152 #9 0x00005555573aaafe in webrtc::ProcessThreadImpl::Process() (this=0x7fffc408daa0) at ../../modules/utility/source/process_thread_impl.cc:257 #10 0x00005555573a8e9b in webrtc::ProcessThreadImpl::<lambda()>::operator()(void) const (__closure=0x7fffc4095e50)at ../../modules/utility/source/process_thread_impl.cc:86

MediaChannel::SendRtp() 最終將 RTP 包發送到網絡的過程與音頻相同，這里不再贅述。視頻的采集、預覽、編碼、發送完整的處理管線如下圖：

黃色的模塊是發生了轉線程的模塊。WebRtcVideoChannel 是子系統的邊界。紫色的模塊為傳輸系統的模塊。

視頻接收處理從創建遠端流的 VideoTrack 開始：

#0 Conductor::OnAddTrack(rtc::scoped_refptr<webrtc::RtpReceiverInterface>, std::vector<rtc::scoped_refptr<webrtc::MediaStreamInterface>, std::allocator<rtc::scoped_refptr<webrtc::MediaStreamInterface> > > const&)(this=0x555556203808 <webrtc::ReturnType<rtc::scoped_refptr<webrtc::RtpReceiverInterface> >::moved_result()+50>, receiver=..., streams=std::vector of length 8088, capacity 8088 = {...}) at ../../examples/peerconnection/client/conductor.cc:218 #1 0x000055555624fbb4 in webrtc::SdpOfferAnswerHandler::ApplyRemoteDescription(std::unique_ptr<webrtc::SessionDescriptionInterface, std::default_delete<webrtc::SessionDescriptionInterface> >, std::map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, cricket::ContentGroup const*, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, cricket::ContentGroup const*> > > const&)(this=0x7fffe40052e0, desc=std::unique_ptr<webrtc::SessionDescriptionInterface> = {...}, bundle_groups_by_mid=std::map with 2 elements = {...})at ../../pc/sdp_offer_answer.cc:1783 #2 0x00005555562546ff in webrtc::SdpOfferAnswerHandler::DoSetRemoteDescription(std::unique_ptr<webrtc::SessionDescriptionInterface, std::default_delete<webrtc::SessionDescriptionInterface> >, rtc::scoped_refptr<webrtc::SetRemoteDescriptionObserverInterface>)(this=0x7fffe40052e0, desc=std::unique_ptr<webrtc::SessionDescriptionInterface> = {...}, observer=...) at ../../pc/sdp_offer_answer.cc:2196 #3 0x000055555624cbbb in webrtc::SdpOfferAnswerHandler::<lambda(std::function<void()>)>::operator()(std::function<void()>)(__closure=0x7fffeeffc340, operations_chain_callback=...) at ../../pc/sdp_offer_answer.cc:1510 #4 0x00005555562813b9 in rtc::rtc_operations_chain_internal::OperationWithFunctor<webrtc::SdpOfferAnswerHandler::SetRemoteDescription(webrtc::SetSessionDescriptionObserver*, webrtc::SessionDescriptionInterface*)::<lambda(std::function<void()>)> >::Run(void) (this=0x7fffe40185b0)at ../../rtc_base/operations_chain.h:71 #5 0x0000555556278f74 in rtc::OperationsChain::ChainOperation<webrtc::SdpOfferAnswerHandler::SetRemoteDescription(webrtc::SetSessionDescriptionObserver*, webrtc::SessionDescriptionInterface*)::<lambda(std::function<void()>)> >(webrtc::SdpOfferAnswerHandler::<lambda(std::function<void()>)> &&)(this=0x7fffe4005600, functor=...) at ../../rtc_base/operations_chain.h:154 #6 0x000055555624ce45 in webrtc::SdpOfferAnswerHandler::SetRemoteDescription(webrtc::SetSessionDescriptionObserver*, webrtc::SessionDescriptionInterface*)(this=0x7fffe40052e0, observer=0x5555589a1a30, desc_ptr=0x555558a224d0) at ../../pc/sdp_offer_answer.cc:1494 #7 0x00005555561cc02f in webrtc::PeerConnection::SetRemoteDescription(webrtc::SetSessionDescriptionObserver*, webrtc::SessionDescriptionInterface*)(this=0x7fffe4004510, observer=0x5555589a1a30, desc_ptr=0x555558a224d0) at ../../pc/peer_connection.cc:1362

然后為遠端視頻流的 VideoTrack 創建渲染器：

#0 GtkMainWnd::VideoRenderer::VideoRenderer(GtkMainWnd*, webrtc::VideoTrackInterface*)(this=0x55555787a349 <cricket::kMediaTypeVideo+5>, main_wnd=0x21, track_to_render=0x55555588bd43 <std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_construct<char const*>(char const*, char const*, std::forward_iterator_tag)+225>)at ../../examples/peerconnection/client/linux/main_wnd.cc:521 #1 0x00005555557b8d0e in GtkMainWnd::StartRemoteRenderer(webrtc::VideoTrackInterface*) (this=0x7fffffffd310, remote_video=0x7fffe40173d0)at ../../examples/peerconnection/client/linux/main_wnd.cc:213 #2 0x00005555557a553f in Conductor::UIThreadCallback(int, void*) (this=0x555558807be0, msg_id=4, data=0x7fffe40173d0)at ../../examples/peerconnection/client/conductor.cc:531 #3 0x00005555557b875e in (anonymous namespace)::HandleUIThreadCallback(gpointer) (data=0x7fffe400ce80)at ../../examples/peerconnection/client/linux/main_wnd.cc:127

從網絡接收編碼視頻數據包：

#0 cricket::WebRtcVideoChannel::OnPacketReceived(rtc::CopyOnWriteBuffer, long)(this=0x5555557d7c73 <rtc::dchecked_cast<long, long>(long)+28>, packet=..., packet_time_us=1640757073828715)at ../../media/engine/webrtc_video_engine.cc:1713 #1 0x0000555556b736fe in cricket::BaseChannel::OnRtpPacket(webrtc::RtpPacketReceived const&) (this=0x7fffc0095950, parsed_packet=...)at ../../pc/channel.cc:467 #2 0x00005555568bec90 in webrtc::RtpDemuxer::OnRtpPacket(webrtc::RtpPacketReceived const&) (this=0x7fffe4006988, packet=...) at ../../call/rtp_demuxer.cc:249 #3 0x0000555556bd5d12 in webrtc::RtpTransport::DemuxPacket(rtc::CopyOnWriteBuffer, long) (this=0x7fffe4006800, packet=..., packet_time_us=1640757073828715)at ../../pc/rtp_transport.cc:194 #4 0x0000555556be0551 in webrtc::SrtpTransport::OnRtpPacketReceived(rtc::CopyOnWriteBuffer, long)(this=0x7fffe4006800, packet=..., packet_time_us=1640757073828715) at ../../pc/srtp_transport.cc:226 #5 0x0000555556bd6898 in webrtc::RtpTransport::OnReadPacket(rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int)(this=0x7fffe4006800, transport=0x7fffe4000ef0, data=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, len=258, packet_time_us=@0x7fffeeffbbc8: 1640757073828715, flags=1) at ../../pc/rtp_transport.cc:268 #6 0x0000555556bd7d41 in sigslot::_opaque_connection::emitter<webrtc::RtpTransport, rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int>(sigslot::_opaque_connection const*, rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int) (self=0x7fffe4004bb0)at ../../rtc_base/third_party/sigslot/sigslot.h:342 #7 0x0000555557276ec7 in sigslot::_opaque_connection::emit<rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int>(rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int) const (this=0x7fffe4004bb0) at ../../rtc_base/third_party/sigslot/sigslot.h:331 #8 0x000055555727656d in sigslot::signal_with_thread_policy<sigslot::single_threaded, rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int>::emit(rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int)(this=0x7fffe4000fe8, args#0=0x7fffe4000ef0, args#1=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, args#2=258, args#3=@0x7fffeeffbbc8: 1640757073828715, args#4=1) at ../../rtc_base/third_party/sigslot/sigslot.h:566 #9 0x0000555557275b90 in sigslot::signal_with_thread_policy<sigslot::single_threaded, rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int>::operator()(rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int)(this=0x7fffe4000fe8, args#0=0x7fffe4000ef0, args#1=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, args#2=258, args#3=@0x7fffeeffbbc8: 1640757073828715, args#4=1) at ../../rtc_base/third_party/sigslot/sigslot.h:570 #10 0x000055555727172e in cricket::DtlsTransport::OnReadPacket(rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int)(this=0x7fffe4000ef0, transport=0x7fffe4003800, data=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, size=258, packet_time_us=@0x7fffeeffbbc8: 1640757073828715, flags=0) at ../../p2p/base/dtls_transport.cc:627 #11 0x0000555557276d64 in sigslot::_opaque_connection::emitter<cricket::DtlsTransport, rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int>(sigslot::_opaque_connection const*, rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int) (self=0x7fffe40031f0)at ../../rtc_base/third_party/sigslot/sigslot.h:342 #12 0x0000555557276ec7 in sigslot::_opaque_connection::emit<rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int>(rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int) const (this=0x7fffe40031f0) at ../../rtc_base/third_party/sigslot/sigslot.h:331 #13 0x000055555727656d in sigslot::signal_with_thread_policy<sigslot::single_threaded, rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int>::emit(rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int)(this=0x7fffe40038f8, args#0=0x7fffe4003800, args#1=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, args#2=258, args#3=@0x7fffeeffbbc8: 1640757073828715, args#4=0) at ../../rtc_base/third_party/sigslot/sigslot.h:566 #14 0x0000555557275b90 in sigslot::signal_with_thread_policy<sigslot::single_threaded, rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int>::operator()(rtc::PacketTransportInternal*, char const*, unsigned long, long const&, int)(this=0x7fffe40038f8, args#0=0x7fffe4003800, args#1=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, args#2=258, args#3=@0x7fffeeffbbc8: 1640757073828715, args#4=0) at ../../rtc_base/third_party/sigslot/sigslot.h:570 #15 0x0000555557295941 in cricket::P2PTransportChannel::OnReadPacket(cricket::Connection*, char const*, unsigned long, long)(this=0x7fffe4003800, connection=0x7fffe401ce90, data=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, len=258, packet_time_us=1640757073828715) at ../../p2p/base/p2p_transport_channel.cc:2215 #16 0x00005555572a4e14 in sigslot::_opaque_connection::emitter<cricket::P2PTransportChannel, cricket::Connection*, char const*, unsigned long, long>(sigslot::_opaque_connection const*, cricket::Connection*, char const*, unsigned long, long) (self=0x7fff84013a40) at ../../rtc_base/third_party/sigslot/sigslot.h:342 #17 0x000055555730fcb0 in sigslot::_opaque_connection::emit<cricket::Connection*, char const*, unsigned long, long>(cricket::Connection*, char const*, unsigned long, long) const (this=0x7fff84013a40) at ../../rtc_base/third_party/sigslot/sigslot.h:331 #18 0x000055555730f612 in sigslot::signal_with_thread_policy<sigslot::single_threaded, cricket::Connection*, char const*, unsigned long, long>::emit(cricket::Connection*, char const*, unsigned long, long)(this=0x7fffe401cf60, args#0=0x7fffe401ce90, args#1=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, args#2=258, args#3=1640757073828715) at ../../rtc_base/third_party/sigslot/sigslot.h:566 #19 0x000055555730ed67 in sigslot::signal_with_thread_policy<sigslot::single_threaded, cricket::Connection*, char const*, unsigned long, long>::operator()(cricket::Connection*, char const*, unsigned long, long)(this=0x7fffe401cf60, args#0=0x7fffe401ce90, args#1=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, args#2=258, args#3=1640757073828715) at ../../rtc_base/third_party/sigslot/sigslot.h:570 #20 0x00005555573004c7 in cricket::Connection::OnReadPacket(char const*, unsigned long, long)(this=0x7fffe401ce90, data=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, size=258, packet_time_us=1640757073828715)at ../../p2p/base/connection.cc:465 #21 0x00005555573134b8 in cricket::UDPPort::OnReadPacket(rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&)(this=0x7fffe401bbb0, socket=0x7fffe4007da0, data=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, size=258, remote_addr=..., packet_time_us=@0x7fffeeffc260: 1640757073828715) at ../../p2p/base/stun_port.cc:394 #22 0x0000555557312fa4 in cricket::UDPPort::HandleIncomingPacket(rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long)(this=0x7fffe401bbb0, socket=0x7fffe4007da0, data=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, size=258, remote_addr=..., packet_time_us=1640757073828715) at ../../p2p/base/stun_port.cc:335 #23 0x00005555572d854f in cricket::AllocationSequence::OnReadPacket(rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&)(this=0x7fffe4001ae0, socket=0x7fffe4007da0, data=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, size=258, remote_addr=..., packet_time_us=@0x7fffeeffc600: 1640757073828715) at ../../p2p/client/basic_port_allocator.cc:1641 #24 0x00005555572e857e in sigslot::_opaque_connection::emitter<cricket::AllocationSequence, rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&>(sigslot::_opaque_connection const*, rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&)(self=0x7fffe40089a0) at ../../rtc_base/third_party/sigslot/sigslot.h:342 #25 0x00005555572eff15 in sigslot::_opaque_connection::emit<rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&>(rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&) const (this=0x7fffe40089a0)at ../../rtc_base/third_party/sigslot/sigslot.h:331 #26 0x00005555572efda3 in sigslot::signal_with_thread_policy<sigslot::single_threaded, rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&>::emit(rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&)(this=0x7fffe4007df0, args#0=0x7fffe4007da0, args#1=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, args#2=258, args#3=..., args#4=@0x7fffeeffc600: 1640757073828715) at ../../rtc_base/third_party/sigslot/sigslot.h:566 #27 0x00005555572efbe0 in sigslot::signal_with_thread_policy<sigslot::single_threaded, rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&>::operator()(rtc::AsyncPacketSocket*, char const*, unsigned long, rtc::SocketAddress const&, long const&)(this=0x7fffe4007df0, args#0=0x7fffe4007da0, args#1=0x7fffe400bba0 "\260aP\"\245\026\300\033?\tT\276", <incomplete sequence \336>, args#2=258, args#3=..., args#4=@0x7fffeeffc600: 1640757073828715) at ../../rtc_base/third_party/sigslot/sigslot.h:570 #28 0x00005555573475ff in rtc::AsyncUDPSocket::OnReadEvent(rtc::Socket*) (this=0x7fffe4007da0, socket=0x7fffe4008ef8)at ../../rtc_base/async_udp_socket.cc:132 #29 0x00005555573477e9 in sigslot::_opaque_connection::emitter<rtc::AsyncUDPSocket, rtc::Socket*>(sigslot::_opaque_connection const*, rtc::Socket*)(self=0x7fffe4008b60) at ../../rtc_base/third_party/sigslot/sigslot.h:342 #30 0x000055555604eb9d in sigslot::_opaque_connection::emit<rtc::Socket*>(rtc::Socket*) const (this=0x7fffe4008b60)at ../../rtc_base/third_party/sigslot/sigslot.h:331 #31 0x000055555604d8e6 in sigslot::signal_with_thread_policy<sigslot::multi_threaded_local, rtc::Socket*>::emit(rtc::Socket*)(this=0x7fffe4008f00, args#0=0x7fffe4008ef8) at ../../rtc_base/third_party/sigslot/sigslot.h:566 #32 0x000055555604ccb5 in sigslot::signal_with_thread_policy<sigslot::multi_threaded_local, rtc::Socket*>::operator()(rtc::Socket*)(this=0x7fffe4008f00, args#0=0x7fffe4008ef8) at ../../rtc_base/third_party/sigslot/sigslot.h:570 #33 0x0000555556047f11 in rtc::SocketDispatcher::OnEvent(unsigned int, int) (this=0x7fffe4008ef0, ff=1, err=0) at ../../rtc_base/physical_socket_server.cc:831 #34 0x00005555560492d4 in rtc::ProcessEvents(rtc::Dispatcher*, bool, bool, bool) (dispatcher=0x7fffe4008ef0, readable=true, writable=false, check_error=false)at ../../rtc_base/physical_socket_server.cc:1222 #35 0x000055555604b232 in rtc::PhysicalSocketServer::WaitEpoll(int) (this=0x7fffe0002cd0, cmsWait=34) at ../../rtc_base/physical_socket_server.cc:1454 #36 0x0000555556049193 in rtc::PhysicalSocketServer::Wait(int, bool) (this=0x7fffe0002cd0, cmsWait=34, process_io=true)at ../../rtc_base/physical_socket_server.cc:1169 #37 0x00005555560546a0 in rtc::Thread::Get(rtc::Message*, int, bool) (this=0x7fffe0001820, pmsg=0x7fffeeffcab0, cmsWait=-1, process_io=true)at ../../rtc_base/thread.cc:547

通常情況下，一個 UDP 包里是放不下一幀編碼視頻數據的，因而在發送端，需要分片，通過多個 RTP 包發出去，而在接收端則需要將這些 RTP 包組幀，組成一個完整的編碼視頻幀。組幀并插入緩沖區的過程如下：

#0 webrtc::video_coding::FrameBuffer::InsertFrame(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >)(this=0x5555557cd6f9 <rtc::safe_cmp_impl::Cmp<rtc::safe_cmp_impl::EqOp, int, int, (void*)0>(int, int)+33>, frame=std::unique_ptr<webrtc::EncodedFrame> = {...}) at ../../modules/video_coding/frame_buffer2.cc:408 #1 0x0000555556a493a5 in webrtc::internal::VideoReceiveStream2::OnCompleteFrame(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >) (this=0x7fffc00b7b50, frame=std::unique_ptr<webrtc::EncodedFrame> = {...}) at ../../video/video_receive_stream2.cc:662 #2 0x0000555556a8d355 in webrtc::RtpVideoStreamReceiver2::OnCompleteFrames(absl::InlinedVector<std::unique_ptr<webrtc::RtpFrameObject, std::default_delete<webrtc::RtpFrameObject> >, 3ul, std::allocator<std::unique_ptr<webrtc::RtpFrameObject, std::default_delete<webrtc::RtpFrameObject> > > >)(this=0x7fffc00b89a8, frames=...) at ../../video/rtp_video_stream_receiver2.cc:868 #3 0x0000555556a8d1e8 in webrtc::RtpVideoStreamReceiver2::OnAssembledFrame(std::unique_ptr<webrtc::RtpFrameObject, std::default_delete<webrtc::RtpFrameObject> >) (this=0x7fffc00b89a8, frame=std::unique_ptr<webrtc::RtpFrameObject> = {...}) at ../../video/rtp_video_stream_receiver2.cc:856 #4 0x0000555556a8cafa in webrtc::RtpVideoStreamReceiver2::OnInsertedPacket(webrtc::video_coding::PacketBuffer::InsertResult)(this=0x7fffc00b89a8, result=...) at ../../video/rtp_video_stream_receiver2.cc:763 #5 0x0000555556a8b284 in webrtc::RtpVideoStreamReceiver2::OnReceivedPayloadData(rtc::CopyOnWriteBuffer, webrtc::RtpPacketReceived const&, webrtc::RTPVideoHeader const&) (this=0x7fffc00b89a8, codec_payload=..., rtp_packet=..., video=...) at ../../video/rtp_video_stream_receiver2.cc:626 #6 0x0000555556a8ec63 in webrtc::RtpVideoStreamReceiver2::ReceivePacket(webrtc::RtpPacketReceived const&) (this=0x7fffc00b89a8, packet=...)at ../../video/rtp_video_stream_receiver2.cc:971 #7 0x0000555556a8b73a in webrtc::RtpVideoStreamReceiver2::OnRecoveredPacket(unsigned char const*, unsigned long)(this=0x7fffc00b89a8, rtp_packet=0x7fffc0120f10 "\220\340%|\242\026\376+z3\252", <incomplete sequence \336>, rtp_packet_length=506)at ../../video/rtp_video_stream_receiver2.cc:649 #8 0x00005555574531ee in webrtc::UlpfecReceiverImpl::ProcessReceivedFec() (this=0x7fffc00ba4f0) at ../../modules/rtp_rtcp/source/ulpfec_receiver_impl.cc:181 #9 0x0000555556a8eddc in webrtc::RtpVideoStreamReceiver2::ParseAndHandleEncapsulatingHeader(webrtc::RtpPacketReceived const&)(this=0x7fffc00b89a8, packet=...) at ../../video/rtp_video_stream_receiver2.cc:989 #10 0x0000555556a8e978 in webrtc::RtpVideoStreamReceiver2::ReceivePacket(webrtc::RtpPacketReceived const&) (this=0x7fffc00b89a8, packet=...)at ../../video/rtp_video_stream_receiver2.cc:956 #11 0x0000555556a8b962 in webrtc::RtpVideoStreamReceiver2::OnRtpPacket(webrtc::RtpPacketReceived const&) (this=0x7fffc00b89a8, packet=...)at ../../video/rtp_video_stream_receiver2.cc:660 #12 0x00005555574bdd45 in webrtc::RtxReceiveStream::OnRtpPacket(webrtc::RtpPacketReceived const&) (this=0x7fffc00d40d0, rtx_packet=...)at ../../call/rtx_receive_stream.cc:77 #13 0x00005555568bec90 in webrtc::RtpDemuxer::OnRtpPacket(webrtc::RtpPacketReceived const&) (this=0x7fffc00904b8, packet=...) at ../../call/rtp_demuxer.cc:249 #14 0x00005555568bae55 in webrtc::RtpStreamReceiverController::OnRtpPacket(webrtc::RtpPacketReceived const&) (this=0x7fffc0090458, packet=...)at ../../call/rtp_stream_receiver_controller.cc:52 #15 0x000055555687916d in webrtc::internal::Call::DeliverRtp(webrtc::MediaType, rtc::CopyOnWriteBuffer, long)(this=0x7fffc0090090, media_type=webrtc::MediaType::VIDEO, packet=..., packet_time_us=1640756514783548) at ../../call/call.cc:1596 #16 0x0000555556879641 in webrtc::internal::Call::DeliverPacket(webrtc::MediaType, rtc::CopyOnWriteBuffer, long)(this=0x7fffc0090090, media_type=webrtc::MediaType::VIDEO, packet=..., packet_time_us=1640756514783548) at ../../call/call.cc:1618 #17 0x00005555560885e2 in cricket::WebRtcVideoChannel::<lambda()>::operator()(void) const (__closure=0x7fffe4070938)at ../../media/engine/webrtc_video_engine.cc:1724 #18 0x00005555560a368e in webrtc::webrtc_new_closure_impl::SafetyClosureTask<cricket::WebRtcVideoChannel::OnPacketReceived(rtc::CopyOnWriteBuffer, int64_t)::<lambda()> >::Run(void) (this=0x7fffe4070930) at ../../rtc_base/task_utils/to_queued_task.h:50

解碼視頻幀：

#0 webrtc::IncomingVideoStream::OnFrame(webrtc::VideoFrame const&)(this=0x5555557d9d0d <std::get<0ul, webrtc::QueuedTask*, std::default_delete<webrtc::QueuedTask> >(std::tuple<webrtc::QueuedTask*, std::default_delete<webrtc::QueuedTask> >&)+28>, video_frame=...) at ../../common_video/incoming_video_stream.cc:37 #1 0x0000555556a65b0f in webrtc::internal::VideoStreamDecoder::FrameToRender(webrtc::VideoFrame&, absl::optional<unsigned char>, int, webrtc::VideoContentType) (this=0x7fffc00d24d0, video_frame=..., qp=..., decode_time_ms=2, content_type=(unknown: 2)) at ../../video/video_stream_decoder2.cc:51 #2 0x00005555574f5e1d in webrtc::VCMDecodedFrameCallback::Decoded(webrtc::VideoFrame&, absl::optional<int>, absl::optional<unsigned char>)(this=0x7fffc00b8728, decodedImage=..., decode_time_ms=..., qp=...) at ../../modules/video_coding/generic_decoder.cc:201 #3 0x0000555556ebb0e7 in webrtc::LibvpxVp8Decoder::ReturnFrame(vpx_image const*, unsigned int, int, webrtc::ColorSpace const*)(this=0x7fffc0091720, img=0x7fff980013a0, timestamp=2718512881, qp=78, explicit_color_space=0x0)at ../../modules/video_coding/codecs/vp8/libvpx_vp8_decoder.cc:367 #4 0x0000555556ebaab6 in webrtc::LibvpxVp8Decoder::Decode(webrtc::EncodedImage const&, bool, long)(this=0x7fffc0091720, input_image=..., missing_frames=false) at ../../modules/video_coding/codecs/vp8/libvpx_vp8_decoder.cc:287 #5 0x00005555574f6806 in webrtc::VCMGenericDecoder::Decode(webrtc::VCMEncodedFrame const&, webrtc::Timestamp) (this=0x7fffc00b88f8, frame=..., now=...)at ../../modules/video_coding/generic_decoder.cc:283 #6 0x00005555574f0284 in webrtc::VideoReceiver2::Decode(webrtc::VCMEncodedFrame const*) (this=0x7fffc00b8668, frame=0x7fffc0109488)at ../../modules/video_coding/video_receiver2.cc:109 #7 0x0000555556a4b41f in webrtc::internal::VideoReceiveStream2::DecodeAndMaybeDispatchEncodedFrame(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >) (this=0x7fffc00b7b50, frame=std::unique_ptr<webrtc::EncodedFrame> = {...}) at ../../video/video_receive_stream2.cc:846 #8 0x0000555556a4afbd in webrtc::internal::VideoReceiveStream2::HandleEncodedFrame(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >) (this=0x7fffc00b7b50, frame=std::unique_ptr<webrtc::EncodedFrame> = {...}) at ../../video/video_receive_stream2.cc:780 #9 0x0000555556a4a712 in webrtc::internal::VideoReceiveStream2::<lambda(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >, webrtc::internal::(anonymous namespace)::ReturnReason)>::operator()(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >, webrtc::internal::(anonymous namespace)::ReturnReason) const(__closure=0x7fffd986a7c0, frame=std::unique_ptr<webrtc::EncodedFrame> = {...}, res=webrtc::video_coding::FrameBuffer::kFrameFound)at ../../video/video_receive_stream2.cc:733 #10 0x0000555556a4d053 in std::_Function_handler<void(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >, webrtc::video_coding::FrameBuffer::ReturnReason), webrtc::internal::VideoReceiveStream2::StartNextDecode()::<lambda(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >, webrtc::internal::(anonymous namespace)::ReturnReason)> >::_M_invoke(const std::_Any_data &, std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> > &&, webrtc::video_coding::FrameBuffer::ReturnReason &&)(__functor=..., __args#0=..., __args#1=@0x7fffd986a6ec: webrtc::video_coding::FrameBuffer::kFrameFound) at /usr/include/c++/9/bits/std_function.h:300 #11 0x00005555574c62b8 in std::function<void (std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >, webrtc::video_coding::FrameBuffer::ReturnReason)>::operator()(std::unique_ptr<webrtc::EncodedFrame, std::default_delete<webrtc::EncodedFrame> >, webrtc::video_coding::FrameBuffer::ReturnReason) const (this=0x7fffd986a7c0, __args#0=std::unique_ptr<webrtc::EncodedFrame> = {...}, __args#1=webrtc::video_coding::FrameBuffer::kFrameFound)at /usr/include/c++/9/bits/std_function.h:688 #12 0x00005555574bec04 in webrtc::video_coding::FrameBuffer::<lambda()>::operator()(void) const (__closure=0x7fff98134698)at ../../modules/video_coding/frame_buffer2.cc:136 #13 0x00005555574c5bbb in webrtc::webrtc_repeating_task_impl::RepeatingTaskImpl<webrtc::video_coding::FrameBuffer::StartWaitForNextFrameOnQueue()::<lambda()> >::RunClosure(void) (this=0x7fff98134670) at ../../rtc_base/task_utils/repeating_task.h:79

視頻流的渲染：

#0 GtkMainWnd::VideoRenderer::OnFrame(webrtc::VideoFrame const&) (this=0x7fffe00176e0, video_frame=...)at ../../examples/peerconnection/client/linux/main_wnd.cc:548 #1 0x0000555556037b5f in rtc::VideoBroadcaster::OnFrame(webrtc::VideoFrame const&) (this=0x7fffe00176b8, frame=...)at ../../media/base/video_broadcaster.cc:90 #2 0x0000555556096029 in cricket::WebRtcVideoChannel::WebRtcVideoReceiveStream::OnFrame(webrtc::VideoFrame const&) (this=0x7fffc00b5200, frame=...)at ../../media/engine/webrtc_video_engine.cc:3105 #3 0x0000555556a483b3 in webrtc::internal::VideoReceiveStream2::OnFrame(webrtc::VideoFrame const&) (this=0x7fffc00b7b50, video_frame=...)at ../../video/video_receive_stream2.cc:591 #4 0x000055555737c24b in webrtc::IncomingVideoStream::Dequeue() (this=0x7fffc00081c0) at ../../common_video/incoming_video_stream.cc:56 #5 0x000055555737bc92 in webrtc::IncomingVideoStream::<lambda()>::operator()(void) (__closure=0x7fff981350d8)at ../../common_video/incoming_video_stream.cc:47 #6 0x000055555737d104 in webrtc::webrtc_new_closure_impl::ClosureTask<webrtc::IncomingVideoStream::OnFrame(const webrtc::VideoFrame&)::<lambda()> >::Run(void) (this=0x7fff981350d0) at ../../rtc_base/task_utils/to_queued_task.h:32

總結

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