在c++中使用directshow过滤器从视频中捕获一帧

我从网上获取了一段代码，从视频文件中捕获一帧，并修改为捕获所有帧并将其存储为bmp图像。

HRESULT GrabVideoBitmap(PCWSTR pszVideoFile)
{
    IGraphBuilder *pGraph = NULL;
    IMediaControl *pControl = NULL;
    IMediaEventEx *pEvent = NULL;
    IBaseFilter *pGrabberF = NULL;
    ISampleGrabber *pGrabber = NULL;
    IBaseFilter *pSourceF = NULL;
    IEnumPins *pEnum = NULL;
    IPin *pPin = NULL;
    IBaseFilter *pNullF = NULL;
    long evCode;
    wchar_t temp[10];
    wchar_t framename[50] = IMAGE_FILE_PATH;    // L"D:\sampleframe";
    BYTE *pBuffer = NULL;
    HRESULT hr = CoInitialize(NULL);
    if (FAILED(hr))
        return 0;
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, 
                          IID_PPV_ARGS(&pGraph));
    hr = pGraph->QueryInterface(IID_PPV_ARGS(&pControl));
    hr = pGraph->QueryInterface(IID_PPV_ARGS(&pEvent));
    // Create the Sample Grabber filter.
    hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER, 
                          IID_PPV_ARGS(&pGrabberF));
    hr = pGraph->AddFilter(pGrabberF, L"Sample Grabber");
    hr = pGrabberF->QueryInterface(IID_PPV_ARGS(&pGrabber));

    // Displays the metadata of the file
    DisplayFileInfo((wchar_t*)pszVideoFile); // to display video information
    AM_MEDIA_TYPE mt;
    ZeroMemory(&mt, sizeof(mt));
    mt.majortype = MEDIATYPE_Video;
    mt.subtype = MEDIASUBTYPE_RGB24;
    hr = pGrabber->SetMediaType(&mt);
    hr = pGraph->AddSourceFilter(pszVideoFile, L"Source", &pSourceF);
    hr = pSourceF->EnumPins(&pEnum);
    while (S_OK == pEnum->Next(1, &pPin, NULL))
    {
        hr = ConnectFilters(pGraph, pPin, pGrabberF);
        SafeRelease(&pPin);
        if (SUCCEEDED(hr))
        {
            break;
        }
    }
    hr = CoCreateInstance(CLSID_NullRenderer, NULL, CLSCTX_INPROC_SERVER,  
                          IID_PPV_ARGS(&pNullF));
    hr = pGraph->AddFilter(pNullF, L"Null Filter");
    hr = ConnectFilters(pGraph, pGrabberF, pNullF);
    hr = pGrabber->SetOneShot(TRUE);
    hr = pGrabber->SetBufferSamples(TRUE);
    hr = pControl->Run();

    hr = pEvent->WaitForCompletion(INFINITE, &evCode);
    for (int i = 0; i < 10; i++)
    {
        // Find the required buffer size.
        long cbBuffer;
        hr = pGrabber->GetCurrentBuffer(&cbBuffer, NULL);
        pBuffer = (BYTE*)CoTaskMemAlloc(cbBuffer);
        hr = pGrabber->GetCurrentBuffer(&cbBuffer, (long*)pBuffer);
        hr = pGrabber->GetConnectedMediaType(&mt);
        // Examine the format block.
        if ((mt.formattype == FORMAT_VideoInfo) &&
            (mt.cbFormat >= sizeof(VIDEOINFOHEADER)) &&
            (mt.pbFormat != NULL))
        {
            swprintf(temp, 5, L"%d", i);
            wcscat_s(framename, temp);
            wcscat_s(framename, L".bmp");
            VIDEOINFOHEADER *pVih = (VIDEOINFOHEADER*)mt.pbFormat;
            hr = WriteBitmap((PCWSTR)framename, &pVih->bmiHeader,  
                  mt.cbFormat - SIZE_PREHEADER, pBuffer, cbBuffer);
            wcscpy_s(framename, IMAGE_FILE_PATH);
        }
        else
        {
            // Invalid format.
            hr = VFW_E_INVALIDMEDIATYPE;
        }
        FreeMediaType(mt);
    }
done:
    CoTaskMemFree(pBuffer);
    SafeRelease(&pPin);
    SafeRelease(&pEnum);
    SafeRelease(&pNullF);
    SafeRelease(&pSourceF);
    SafeRelease(&pGrabber);
    SafeRelease(&pGrabberF);
    SafeRelease(&pControl);
    SafeRelease(&pEvent);
    SafeRelease(&pGraph);
    return hr;
}

输入的视频文件有132帧。但是只生成了68张图像。最后38张图像的最后一帧视频也被捕获。

我认为directshow图形正在连续运行，而WriteBitmap()缺少帧。

如何在directX中获得控件捕获一帧并将其写入bmp文件并捕获下一帧，从而捕获所有帧为bmp图像

谢谢阿伦