IVMRMixerControl9为何QueryInterface不成功呢

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
  }

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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～ 
[解决办法]
CoInitialize(NULL)
[解决办法]