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

VideoCaptureDS::Init

int32_t VideoCaptureDS::Init(const char* deviceUniqueIdUTF8) {
***
  // Temporary connect here.
  // This is done so that no one else can use the capture device.
  if (SetCameraOutput(_requestedCapability) != 0) {
    return -1;
  }
****
  return 0;
}

—》

VideoCaptureDS::SetCameraOutput

int32_t VideoCaptureDS::SetCameraOutput(
    const VideoCaptureCapability& requestedCapability) {
  // Get the best matching capability
  VideoCaptureCapability capability;
  int32_t capabilityIndex;
  // Store the new requested size
  _requestedCapability = requestedCapability;
  //1、 Match the requested capability with the supported.
  // 先调用CreateCapabilityMap获取系统支持的所有capability，然后寻找最佳的capability的索引
  if ((capabilityIndex = _dsInfo.GetBestMatchedCapability(
           _deviceUniqueId, _requestedCapability, capability)) < 0) {
    return -1;
  }
  //2、 Reduce the frame rate if possible.
  if (capability.maxFPS > requestedCapability.maxFPS) {
    capability.maxFPS = requestedCapability.maxFPS;
  } else if (capability.maxFPS <= 0) {
    capability.maxFPS = 30;
  }
  //2、 Convert it to the windows capability index since they are not nexessary
  // the same 
   // 根据索引，获取最佳capability
  VideoCaptureCapabilityWindows windowsCapability;
  if (_dsInfo.GetWindowsCapability(capabilityIndex, windowsCapability) != 0) {
    return -1;
  }
  IAMStreamConfig* streamConfig = NULL;
  AM_MEDIA_TYPE* pmt = NULL;
  VIDEO_STREAM_CONFIG_CAPS caps;
  HRESULT hr = _outputCapturePin->QueryInterface(IID_IAMStreamConfig,
                                                 (void**)&streamConfig);
  if (hr) {
    RTC_LOG(LS_INFO) << "Can't get the Capture format settings.";
    return -1;
  }
  // Get the windows capability from the capture device
  // 从采集设备获取系统 capability，用于修改
  bool isDVCamera = false;
  hr = streamConfig->GetStreamCaps(windowsCapability.directShowCapabilityIndex,
                                   &pmt, reinterpret_cast<BYTE*>(&caps));
  if (hr == S_OK) {
    if (pmt->formattype == FORMAT_VideoInfo2) {
      VIDEOINFOHEADER2* h = reinterpret_cast<VIDEOINFOHEADER2*>(pmt->pbFormat);
      if (capability.maxFPS > 0 && windowsCapability.supportFrameRateControl) {
        h->AvgTimePerFrame = REFERENCE_TIME(10000000.0 / capability.maxFPS);
      }
    } else { // 本机是这个类型
      VIDEOINFOHEADER* h = reinterpret_cast<VIDEOINFOHEADER*>(pmt->pbFormat);
      if (capability.maxFPS > 0 && windowsCapability.supportFrameRateControl) {
        h->AvgTimePerFrame = REFERENCE_TIME(10000000.0 / capability.maxFPS);
      }
    }
    // Set the sink filter to request this capability
    // 设置capability到filter
    sink_filter_->SetRequestedCapability(capability);
    // Order the capture device to use this capability
      // 设置最终的格式
    hr += streamConfig->SetFormat(pmt);
    // Check if this is a DV camera and we need to add MS DV Filter
    if (pmt->subtype == MEDIASUBTYPE_dvsl ||
        pmt->subtype == MEDIASUBTYPE_dvsd || pmt->subtype == MEDIASUBTYPE_dvhd)
      isDVCamera = true;  // This is a DV camera. Use MS DV filter
  }
  RELEASE_AND_CLEAR(streamConfig);
  if (FAILED(hr)) {
    RTC_LOG(LS_INFO) << "Failed to set capture device output format";
    return -1;
  }
  if (isDVCamera) {
    hr = ConnectDVCamera();
  } else {
      // 调用后，后面会进去CaptureInputPin::ReceiveConnection
    hr = _graphBuilder->ConnectDirect(_outputCapturePin, _inputSendPin, NULL);
  }
  if (hr != S_OK) {
    RTC_LOG(LS_INFO) << "Failed to connect the Capture graph " << hr;
    return -1;
  }
  return 0;
}

-》1、_dsInfo.GetBestMatchedCapability

DeviceInfoImpl::GetBestMatchedCapability

int32_t DeviceInfoImpl::GetBestMatchedCapability(
    const char* deviceUniqueIdUTF8,
    const VideoCaptureCapability& requested, // 可修改
    VideoCaptureCapability& resulting) {  //可以修改
  if (!deviceUniqueIdUTF8)
    return -1;
  MutexLock lock(&_apiLock);
  if (!absl::EqualsIgnoreCase(
          deviceUniqueIdUTF8,
          absl::string_view(_lastUsedDeviceName, _lastUsedDeviceNameLength))) {
    if (-1 == CreateCapabilityMap(deviceUniqueIdUTF8)) {
      return -1;
    }
  }
    // 下面的是获取跟想要设备的Capability最接近的Capability
  int32_t bestformatIndex = -1;
  int32_t bestWidth = 0;
  int32_t bestHeight = 0;
  int32_t bestFrameRate = 0;
  VideoType bestVideoType = VideoType::kUnknown;
  const int32_t numberOfCapabilies =
      static_cast<int32_t>(_captureCapabilities.size());
  for (int32_t tmp = 0; tmp < numberOfCapabilies;
       ++tmp)  // Loop through all capabilities
  {
    VideoCaptureCapability& capability = _captureCapabilities[tmp];
    const int32_t diffWidth = capability.width - requested.width;
    const int32_t diffHeight = capability.height - requested.height;
    const int32_t diffFrameRate = capability.maxFPS - requested.maxFPS;
    const int32_t currentbestDiffWith = bestWidth - requested.width;
    const int32_t currentbestDiffHeight = bestHeight - requested.height;
    const int32_t currentbestDiffFrameRate = bestFrameRate - requested.maxFPS;
    if ((diffHeight >= 0 &&
         diffHeight <= abs(currentbestDiffHeight))  // Height better or equalt
                                                    // that previouse.
        || (currentbestDiffHeight < 0 && diffHeight >= currentbestDiffHeight)) {
      if (diffHeight ==
          currentbestDiffHeight)  // Found best height. Care about the width)
      {
        if ((diffWidth >= 0 &&
             diffWidth <= abs(currentbestDiffWith))  // Width better or equal
            || (currentbestDiffWith < 0 && diffWidth >= currentbestDiffWith)) {
          if (diffWidth == currentbestDiffWith &&
              diffHeight == currentbestDiffHeight)  // Same size as previously
          {
            // Also check the best frame rate if the diff is the same as
            // previouse
            if (((diffFrameRate >= 0 &&
                  diffFrameRate <=
                      currentbestDiffFrameRate)  // Frame rate to high but
                                                 // better match than previouse
                                                 // and we have not selected IUV
                 || (currentbestDiffFrameRate < 0 &&
                     diffFrameRate >=
                         currentbestDiffFrameRate))  // Current frame rate is
                                                     // lower than requested.
                                                     // This is better.
            ) {
              if ((currentbestDiffFrameRate ==
                   diffFrameRate)  // Same frame rate as previous  or frame rate
                                   // allready good enough
                  || (currentbestDiffFrameRate >= 0)) {
                if (bestVideoType != requested.videoType &&
                    requested.videoType != VideoType::kUnknown &&
                    (capability.videoType == requested.videoType ||
                     capability.videoType == VideoType::kI420 ||
                     capability.videoType == VideoType::kYUY2 ||
                     capability.videoType == VideoType::kYV12)) {
                  bestVideoType = capability.videoType;
                  bestformatIndex = tmp;
                }
                // If width height and frame rate is full filled we can use the
                // camera for encoding if it is supported.
                if (capability.height == requested.height &&
                    capability.width == requested.width &&
                    capability.maxFPS >= requested.maxFPS) {
                  bestformatIndex = tmp;
                }
              } else  // Better frame rate
              {
                bestWidth = capability.width;
                bestHeight = capability.height;
                bestFrameRate = capability.maxFPS;
                bestVideoType = capability.videoType;
                bestformatIndex = tmp;
              }
            }
          } else  // Better width than previously
          {
            bestWidth = capability.width;
            bestHeight = capability.height;
            bestFrameRate = capability.maxFPS;
            bestVideoType = capability.videoType;
            bestformatIndex = tmp;
          }
        }     // else width no good
      } else  // Better height
      {
        bestWidth = capability.width;
        bestHeight = capability.height;
        bestFrameRate = capability.maxFPS;
        bestVideoType = capability.videoType;
        bestformatIndex = tmp;
      }
    }  // else height not good
  }    // end for
  RTC_LOG(LS_VERBOSE) << "Best camera format: " << bestWidth << "x"
                      << bestHeight << "@" << bestFrameRate
                      << "fps, color format: "
                      << static_cast<int>(bestVideoType);
  // Copy the capability
  if (bestformatIndex < 0)
    return -1;
  resulting = _captureCapabilities[bestformatIndex];
  return bestformatIndex;
}
// Default implementation. This should be overridden by Mobile implementations.
int32_t DeviceInfoImpl::GetOrientation(const char* deviceUniqueIdUTF8,
                                       VideoRotation& orientation) {
  orientation = kVideoRotation_0;
  return -1;
}

里面调用 DeviceInfoDS::CreateCapabilityMap

int32_t DeviceInfoDS::CreateCapabilityMap(const char* deviceUniqueIdUTF8)
{
  // Reset old capability list
  _captureCapabilities.clear();
  const int32_t deviceUniqueIdUTF8Length =
      (int32_t)strlen((char*)deviceUniqueIdUTF8);
  if (deviceUniqueIdUTF8Length > kVideoCaptureUniqueNameLength) {
    RTC_LOG(LS_INFO) << "Device name too long";
    return -1;
  }
  RTC_LOG(LS_INFO) << "CreateCapabilityMap called for device "
                   << deviceUniqueIdUTF8;
  char productId[kVideoCaptureProductIdLength];
  IBaseFilter* captureDevice = DeviceInfoDS::GetDeviceFilter(
      deviceUniqueIdUTF8, productId, kVideoCaptureProductIdLength);
  if (!captureDevice)
    return -1;
  IPin* outputCapturePin = GetOutputPin(captureDevice, GUID_NULL);
  if (!outputCapturePin) {
    RTC_LOG(LS_INFO) << "Failed to get capture device output pin";
    RELEASE_AND_CLEAR(captureDevice);
    return -1;
  }
  IAMExtDevice* extDevice = NULL;
  HRESULT hr =
      captureDevice->QueryInterface(IID_IAMExtDevice, (void**)&extDevice);
  if (SUCCEEDED(hr) && extDevice) {
    RTC_LOG(LS_INFO) << "This is an external device";
    extDevice->Release();
  }
  IAMStreamConfig* streamConfig = NULL;
  hr = outputCapturePin->QueryInterface(IID_IAMStreamConfig,
                                        (void**)&streamConfig);
  if (FAILED(hr)) {
    RTC_LOG(LS_INFO) << "Failed to get IID_IAMStreamConfig interface "
                        "from capture device";
    return -1;
  }
  // this  gets the FPS
  IAMVideoControl* videoControlConfig = NULL;
  HRESULT hrVC = captureDevice->QueryInterface(IID_IAMVideoControl,
                                               (void**)&videoControlConfig);
  if (FAILED(hrVC)) {
    RTC_LOG(LS_INFO) << "IID_IAMVideoControl Interface NOT SUPPORTED";
  }
  AM_MEDIA_TYPE* pmt = NULL;
  VIDEO_STREAM_CONFIG_CAPS caps;
  int count, size;
   // 这里本机调试的count=5, size=128
    // 一共有5个Capabilities，每个fCapabilities占用空间128字节
  hr = streamConfig->GetNumberOfCapabilities(&count, &size);
  if (FAILED(hr)) {
    RTC_LOG(LS_INFO) << "Failed to GetNumberOfCapabilities";
    RELEASE_AND_CLEAR(videoControlConfig);
    RELEASE_AND_CLEAR(streamConfig);
    RELEASE_AND_CLEAR(outputCapturePin);
    RELEASE_AND_CLEAR(captureDevice);
    return -1;
  }
  // Check if the device support formattype == FORMAT_VideoInfo2 and
  // FORMAT_VideoInfo. Prefer FORMAT_VideoInfo since some cameras (ZureCam) has
  // been seen having problem with MJPEG and FORMAT_VideoInfo2 Interlace flag is
  // only supported in FORMAT_VideoInfo2
  bool supportFORMAT_VideoInfo2 = false;
  bool supportFORMAT_VideoInfo = false;
  bool foundInterlacedFormat = false;
  GUID preferedVideoFormat = FORMAT_VideoInfo;
  for (int32_t tmp = 0; tmp < count; ++tmp) {
    hr = streamConfig->GetStreamCaps(tmp, &pmt, reinterpret_cast<BYTE*>(&caps));
    if (hr == S_OK) {
      if (pmt->majortype == MEDIATYPE_Video &&
          pmt->formattype == FORMAT_VideoInfo2) {
     ****
      }
      if (pmt->majortype == MEDIATYPE_Video &&
          pmt->formattype == FORMAT_VideoInfo) {
        RTC_LOG(LS_INFO) << "Device support FORMAT_VideoInfo2";
        supportFORMAT_VideoInfo = true; // 本机只支持这个
      }
    }
  }
  if (supportFORMAT_VideoInfo2) {
    if (supportFORMAT_VideoInfo && !foundInterlacedFormat) {
      preferedVideoFormat = FORMAT_VideoInfo;
    } else {
      preferedVideoFormat = FORMAT_VideoInfo2;
    }
  }
  for (int32_t tmp = 0; tmp < count; ++tmp) {
    hr = streamConfig->GetStreamCaps(tmp, &pmt, reinterpret_cast<BYTE*>(&caps));
    if (hr != S_OK) {
      RTC_LOG(LS_INFO) << "Failed to GetStreamCaps";
      RELEASE_AND_CLEAR(videoControlConfig);
      RELEASE_AND_CLEAR(streamConfig);
      RELEASE_AND_CLEAR(outputCapturePin);
      RELEASE_AND_CLEAR(captureDevice);
      return -1;
    }
    if (pmt->majortype == MEDIATYPE_Video &&
        pmt->formattype == preferedVideoFormat) {
      VideoCaptureCapabilityWindows capability;
      int64_t avgTimePerFrame = 0;
      if (pmt->formattype == FORMAT_VideoInfo) {
        VIDEOINFOHEADER* h = reinterpret_cast<VIDEOINFOHEADER*>(pmt->pbFormat);
        assert(h);
        capability.directShowCapabilityIndex = tmp;
        capability.width = h->bmiHeader.biWidth;
        capability.height = h->bmiHeader.biHeight;
        avgTimePerFrame = h->AvgTimePerFrame;
      }
     ***
      if (hrVC == S_OK) {
        LONGLONG* frameDurationList;
        LONGLONG maxFPS;
        long listSize;
        SIZE size;
        size.cx = capability.width;
        size.cy = capability.height;
        // GetMaxAvailableFrameRate doesn't return max frame rate always
        // eg: Logitech Notebook. This may be due to a bug in that API
        // because GetFrameRateList array is reversed in the above camera. So
        // a util method written. Can't assume the first value will return
        // the max fps.
        hrVC = videoControlConfig->GetFrameRateList(
            outputCapturePin, tmp, size, &listSize, &frameDurationList);
        // On some odd cameras, you may get a 0 for duration.
        // GetMaxOfFrameArray returns the lowest duration (highest FPS)
        if (hrVC == S_OK && listSize > 0 &&
            0 != (maxFPS = GetMaxOfFrameArray(frameDurationList, listSize))) {
          capability.maxFPS = static_cast<int>(10000000 / maxFPS); // 本机是30fps
          capability.supportFrameRateControl = true;
        }
          ****
      // can't switch MEDIATYPE :~(
      if (pmt->subtype == MEDIASUBTYPE_I420) {
        capability.videoType = VideoType::kI420;
      } else if (pmt->subtype == MEDIASUBTYPE_IYUV) {
        capability.videoType = VideoType::kIYUV;
      } else if (pmt->subtype == MEDIASUBTYPE_RGB24) {
        capability.videoType = VideoType::kRGB24;
      } else if (pmt->subtype == MEDIASUBTYPE_YUY2) {
        capability.videoType = VideoType::kYUY2; // 本机支持这个适配类型
      } else if (pmt->subtype == MEDIASUBTYPE_RGB565) {
        capability.videoType = VideoType::kRGB565;
      } else if (pmt->subtype == MEDIASUBTYPE_MJPG) {
        capability.videoType = VideoType::kMJPEG;
      } 
          ****
      _captureCapabilities.push_back(capability);
      _captureCapabilitiesWindows.push_back(capability);
      RTC_LOG(LS_INFO) << "Camera capability, width:" << capability.width
                       << " height:" << capability.height
                       << " type:" << static_cast<int>(capability.videoType)
                       << " fps:" << capability.maxFPS;
    }
    FreeMediaType(pmt);
    pmt = NULL;
  }
****
  return static_cast<int32_t>(_captureCapabilities.size());
}

—》2、_dsInfo.GetWindowsCapability(capabilityIndex, windowsCapability)

DeviceInfoDS::GetWindowsCapability

int32_t DeviceInfoDS::GetWindowsCapability(
    const int32_t capabilityIndex,
    VideoCaptureCapabilityWindows& windowsCapability) {
  MutexLock lock(&_apiLock);
  if (capabilityIndex < 0 || static_cast<size_t>(capabilityIndex) >=
                                 _captureCapabilitiesWindows.size()) {
    return -1;
  }
  windowsCapability = _captureCapabilitiesWindows[capabilityIndex];
  return 0;
}

—》3、 hr = _graphBuilder->ConnectDirect(_outputCapturePin, _inputSendPin, NULL);
调用后，会进入CaptureInputPin::ReceiveConnection

CaptureInputPin::ReceiveConnection

里面会判断是否会支持这个连接

STDMETHODIMP CaptureInputPin::ReceiveConnection(
    IPin* connector,
    const AM_MEDIA_TYPE* media_type) {
  RTC_DCHECK_RUN_ON(&main_checker_);
  RTC_DCHECK(Filter()->IsStopped());
  if (receive_pin_) {
    RTC_DCHECK(false);
    return VFW_E_ALREADY_CONNECTED;
  }
  HRESULT hr = CheckDirection(connector);
  if (FAILED(hr))
    return hr;
    // 将media_type，转为resulting_capability_
  if (!TranslateMediaTypeToVideoCaptureCapability(media_type,
                                                  &resulting_capability_))
    return VFW_E_TYPE_NOT_ACCEPTED;
  // Complete the connection
  receive_pin_ = connector;
  ResetMediaType(&media_type_);
  CopyMediaType(&media_type_, media_type);
  return S_OK;
}

该函数返回后，就好开始创建内存分配器了CaptureInputPin::GetAllocator