前言

H:\webrtc-20210315\webrtc-20210315\webrtc\webrtc-checkout\src\modules\video_capture\windows\help_functions_ds.cc
hr = pKs->Get(AMPROPSETID_Pin, AMPROPERTY_PIN_CATEGORY, NULL, 0,
&PinCategory, sizeof(GUID), &cbReturned);

代码分析

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) {
 ***
  _outputCapturePin = GetOutputPin(_captureFilter, PIN_CATEGORY_CAPTURE);
  if (!_outputCapturePin) {
    RTC_LOG(LS_INFO) << "Failed to get output capture pin";
    return -1;
  }
 ***
}

—》H:\webrtc-20210315\webrtc-20210315\webrtc\webrtc-checkout\src\modules\video_capture\windows\help_functions_ds.cc

GetOutputPin

IPin* GetOutputPin(IBaseFilter* filter, REFGUID Category) {
  HRESULT hr;
  IPin* pin = NULL;
  IEnumPins* pPinEnum = NULL;
  filter->EnumPins(&pPinEnum);
  if (pPinEnum == NULL) {
    return NULL;
  }
  // get first unconnected pin
  hr = pPinEnum->Reset();  // set to first pin
  while (S_OK == pPinEnum->Next(1, &pin, NULL)) {
    PIN_DIRECTION pPinDir;
    pin->QueryDirection(&pPinDir);
    if (PINDIR_OUTPUT == pPinDir)  // This is an output pin
    { // 我们就是要获取输出的pin，这里的GUID_NULL表示任意类型
      if (Category == GUID_NULL || PinMatchesCategory(pin, Category)) {
        pPinEnum->Release();
        return pin;
      }
    }
    pin->Release();
    pin = NULL;
  }
  pPinEnum->Release();
  return NULL;
}

—》PinMatchesCategory(pin, Category)

PinMatchesCategory

BOOL PinMatchesCategory(IPin* pPin, REFGUID Category) {
  BOOL bFound = FALSE;
  IKsPropertySet* pKs = NULL;
  // 获取该IKsPropertySet接口
  HRESULT hr = pPin->QueryInterface(IID_PPV_ARGS(&pKs));
  if (SUCCEEDED(hr)) {
    GUID PinCategory;
    DWORD cbReturned;
    hr = pKs->Get(AMPROPSETID_Pin, AMPROPERTY_PIN_CATEGORY, NULL, 0,
                  &PinCategory, sizeof(GUID), &cbReturned);
    if (SUCCEEDED(hr) && (cbReturned == sizeof(GUID))) {
        // 如果PinCategory等于输入的Category，则说明已经找到了匹配的pin
      bFound = (PinCategory == Category);
    }
    pKs->Release();
  }
  return bFound;
}

调用堆栈