IVMRMixerControl9为什么QueryInterface不成功呢？解决办法

IVMRMixerControl9为什么QueryInterface不成功呢？
IBaseFilter* pVmr = NULL;

  // Create the VMR and add it to the filter graph.
  HRESULT hr = CoCreateInstance(CLSID_VideoMixingRenderer, NULL,
  CLSCTX_INPROC, IID_IBaseFilter, (void**)&pVmr);




  if (SUCCEEDED(hr)) 
  {
  hr = m_pGB->AddFilter(pVmr, L"Video Mixing Renderer");
  if (SUCCEEDED(hr)) 
  {
  // Set the rendering mode and number of streams.  
  IVMRFilterConfig* pConfig;

  hr = pVmr->QueryInterface(IID_IVMRFilterConfig, (void**)&pConfig);
  if( SUCCEEDED(hr)) 
  {
  pConfig->SetRenderingMode(VMRMode_Windowless);
  pConfig->Release();
  }

  hr = pVmr->QueryInterface(IID_IVMRWindowlessControl, (void**)&m_pWC);
  if( SUCCEEDED(hr)) 
  {
  m_pWC->SetVideoClippingWindow(hWnd);
   
  }


hr = pVmr->QueryInterface(IID_IVMRMixerControl9, (void**)&m_pMixerC);
if (FAILED(hr))
{
AfxMessageBox("error");//就在错误！总是FAILED
}

================================================
我想用dshow来抓图，并实现图象的色度，亮度调节 ，想用IVMRMixerControl9接口的
SetProcAmpControl 来做！得QueryInterface总是不成功，是什么原因呢？
或者哪位知道可以用VC来做摄像头抓图并可以调节亮度的例子或代码，多谢了～

------解决方案--------------------------------------------------------
CoInitialize(NULL)
------解决方案--------------------------------------------------------

探讨

和这没关系的吧CoInitialize(NULL)
上面几个QueryInterface 都SUCCEEDED的啊！