一个关于DirectShow的有关问题

void main(){
    HRESULT hr = CoInitialize(NULL);
    if (FAILED(hr))
    {
        // Add error-handling code here. (Omitted for clarity.)
    }
    IGraphBuilder *pGraph;
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, 
    CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&pGraph);
    IMediaControl *pControl;
    IMediaEvent   *pEvent;
    IMpegAudioDecoder *pDecoder;
    IBaseFilter *pFilter;
    pFilter=NULL;    
    hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
    hr = pGraph->AddFilter(pFilter,L"Source");    
    hr = pFilter->QueryInterface(IID_IMpegAudioDecoder,(void **)&pDecoder);//注意：这行报错。
    hr = pDecoder->put_DualMode(AM_MPEG_AUDIO_DUAL_RIGHT);    
    hr = pGraph->RenderFile(L"C:\\123.dat", NULL);    
    hr = pControl->Run();    
}