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H:\webrtc-20210315\webrtc-20210315\webrtc\webrtc-checkout\src\modules\video_capture\windows\video_capture_ds.cc

VideoCaptureDS::Init()

  1. int32_t VideoCaptureDS::Init(const char* deviceUniqueIdUTF8) {
  2.   const int32_t nameLength = (int32_t)strlen((char*)deviceUniqueIdUTF8);
  3.   if (nameLength > kVideoCaptureUniqueNameLength)
  4.     return -1;
  6.   // Store the device name
  7.   _deviceUniqueId = new (std::nothrow) char[nameLength + 1];
  8.   memcpy(_deviceUniqueId, deviceUniqueIdUTF8, nameLength + 1);
  10.   if (_dsInfo.Init() != 0)
  11.     return -1;
  13.   _captureFilter = _dsInfo.GetDeviceFilter(deviceUniqueIdUTF8);
  14.   if (!_captureFilter) {
  15.     RTC_LOG(LS_INFO) << "Failed to create capture filter.";
  16.     return -1;
  17.   }
  19.   // Get the interface for DirectShow's GraphBuilder
  20.   HRESULT hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER,
  21.                                 IID_IGraphBuilder, (void**)&_graphBuilder);
  22.   if (FAILED(hr)) {
  23.     RTC_LOG(LS_INFO) << "Failed to create graph builder.";
  24.     return -1;
  25.   }
  27.   hr = _graphBuilder->QueryInterface(IID_IMediaControl, (void**)&_mediaControl);
  28.   if (FAILED(hr)) {
  29.     RTC_LOG(LS_INFO) << "Failed to create media control builder.";
  30.     return -1;
  31.   }
  32.   hr = _graphBuilder->AddFilter(_captureFilter, CAPTURE_FILTER_NAME);
  33.   if (FAILED(hr)) {
  34.     RTC_LOG(LS_INFO) << "Failed to add the capture device to the graph.";
  35.     return -1;
  36.   }
  38.   _outputCapturePin = GetOutputPin(_captureFilter, PIN_CATEGORY_CAPTURE);
  39.   if (!_outputCapturePin) {
  40.     RTC_LOG(LS_INFO) << "Failed to get output capture pin";
  41.     return -1;
  42.   }
  44.   // Create the sink filte used for receiving Captured frames.
  45.   sink_filter_ = new ComRefCount<CaptureSinkFilter>(this);
  47.   hr = _graphBuilder->AddFilter(sink_filter_, SINK_FILTER_NAME);
  48.   if (FAILED(hr)) {
  49.     RTC_LOG(LS_INFO) << "Failed to add the send filter to the graph.";
  50.     return -1;
  51.   }
  53.   _inputSendPin = GetInputPin(sink_filter_);
  54.   if (!_inputSendPin) {
  55.     RTC_LOG(LS_INFO) << "Failed to get input send pin";
  56.     return -1;
  57.   }
  59.   // Temporary connect here.
  60.   // This is done so that no one else can use the capture device.
  61.   if (SetCameraOutput(_requestedCapability) != 0) {
  62.     return -1;
  63.   }
  65.   hr = _mediaControl->Pause();
  66.   if (FAILED(hr)) {
  67.     RTC_LOG(LS_INFO)
  68.         << "Failed to Pause the Capture device. Is it already occupied? " << hr;
  69.     return -1;
  70.   }
  71.   RTC_LOG(LS_INFO) << "Capture device '" << deviceUniqueIdUTF8
  72.                    << "' initialized.";
  73.   return 0;
  74. }

通过DeviceInfo::GetDeviceFilter就可以采集视频数据了。
IGraphBuilder做了两件事：
1、创建IMediaControl，控制啥时候开始或停止采集视频数据
2、AddFilter添加Filter到FilterGraph，接收采集数据传输到上层