c++ - 将 SampleGrabber 与 CaptureGraphBuilder2 结合使用时出现问题

Question

我一直在尝试使用 SampleGrabber 从网络摄像头抓取帧并将其保存为位图，但一直没有成功。我使用 ICaptureGraphBuilder2 在 MSDN 上使用了 Directshow 视频捕获示例以及示例抓取器示例。

我希望我的过滤图看起来像下面这样:

网络摄像头(来源)-> 样本采集器-> 空渲染器

由于我对预览不感兴趣，所以我认为空渲染器对我来说就足够了。

计划是通过搜索特定的 VID 和 PID (webcamCapture::findWebCam()) 来找到我的网络摄像头，创建我的样本采集器，创建空渲染器，然后使用 pGraphBuilder->RenderStream() 将它们连接在一起。由于我只需要一帧，因此我使用了 OneShot 方法，然后使用 GetCurrentBuffer 来检索帧。

问题出现在这一行:

pEvent->WaitForCompletion(2000, &evCode);

返回的 HRESULT 代码是 E_ABORT。将超时设置为 INFINITE 会导致程序卡住，这可能意味着过滤器永远不会停止。 pControl->Run() 的 HRESULT 是 S_FALSE，这意味着并非所有过滤器都在运行。我不确定为什么会这样，我感觉在构建这些过滤器时出了点问题。

下面是我的来源转储。我创建了一个类来处理网络摄像头捕获。在使用中，基本上有两件事被调用:

webcamCapture::buildFilterGraph()
webcamCapture::runFilter()

runFilter 将运行过滤器并将帧保存为位图文件。我是 directshow 的新手，我很确定我错过了一些简单的东西。任何见解将不胜感激!

来源

    HRESULT webcamCapture::buildFilterGraph(void){
    HRESULT hr;

    if (FAILED(hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED))) {
        return hr;
    }

    createCOMInstances();

    //  Use findWebCam() to find the webcam and add it to our capture graph
    hr = findWebCam();
    if(FAILED(hr)){
        return hr;
    }

    //  Add the sample grabber to the graph
    hr = pGraph->AddFilter(pGrabberF, L"Sample Grabber");
    if(FAILED(hr)){
        return hr;
    }

    hr = pGrabberF->QueryInterface(IID_PPV_ARGS(&pGrabber));
    if(FAILED(hr)){
        return hr;
    }

    //  Set media type for the sample grabber (24-bit RGB Uncompressed video)
    ZeroMemory(&mt, sizeof(mt));
    mt.majortype = MEDIATYPE_Video;
    mt.subtype = MEDIASUBTYPE_RGB24;

    hr = pGrabber->SetMediaType(&mt);
    if(FAILED(hr)){
        return hr;
    }

    hr = pGraph->AddFilter(pNullF, L"Null Filter");
    if(FAILED(hr)){
        return hr;
    }

    //  Connect source (pCapF), sample grabber (pGrabberF) and null renderer (pNullF)
    pGraphBuilder->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, pCapF,pGrabberF, pNullF);

    hr = pGrabber->SetOneShot(TRUE);
    hr = pGrabber->SetBufferSamples(TRUE);


    return S_OK;
    }

    HRESULT webcamCapture::runFilter(){
    HRESULT hr;
    FILTER_STATE filterState;

    pBuffer = NULL;



    hr = pControl->Run();
    if(FAILED(hr)){
        goto done;
    }

    pControl->GetState(1000, (OAFilterState*)&filterState);

    long evCode;
    hr = pEvent->WaitForCompletion(2000, &evCode);
    if(FAILED(hr)){
        goto done;
    }

    long cbBuffer;
    hr = pGrabber->GetCurrentBuffer(&cbBuffer, NULL);
    if(FAILED(hr)){
        goto done;
    }

    pBuffer = (BYTE*)CoTaskMemAlloc(cbBuffer);
    if(!pBuffer){
        hr = E_OUTOFMEMORY;
        goto done;
    }

    hr = pGrabber->GetCurrentBuffer(&cbBuffer, (long*)pBuffer);
    if(FAILED(hr)){
        goto done;
    }

    hr = pGrabber->GetConnectedMediaType(&mt);
    if(FAILED(hr)){
        goto done;
    }

    if((mt.formattype == FORMAT_VideoInfo) && (mt.cbFormat >= sizeof(VIDEOINFOHEADER)) && (mt.pbFormat != NULL)){

        VIDEOINFOHEADER *pVih = (VIDEOINFOHEADER*)mt.pbFormat;
        writeBitmap(L"test_image.bmp", &pVih->bmiHeader, mt.cbFormat - SIZE_PREHEADER, pBuffer, cbBuffer);
    }

    //FreeMediaType(mt);

    done:
        CoTaskMemFree(pBuffer);
        pNullF->Release();
        pNullF = NULL;
        pCapF->Release();
        pCapF = NULL;
        pGrabber->Release();
        pGrabber = NULL;
        pGrabberF->Release();
        pGrabberF = NULL;
        pControl->Release();
        pControl = NULL;
        pEvent->Release();
        pEvent = NULL;
        pGraph->Release();
        pGraph = NULL;
        CoUninitialize();


    return hr;
    }

    HRESULT webcamCapture::createCOMInstances(void){
    HRESULT hr;

    //  Instructions to create a Capture Graph using CaptureGraphBuilder2 can be found at https://msdn.microsoft.com/en-us/library/windows/desktop/dd373396(v=vs.85).aspx

    //  Create Capture Graph Builder
    hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pGraphBuilder));
    if(FAILED(hr)){
        return hr;
    }

    //  Create Graph Manager
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pGraph));
    if(FAILED(hr)){
        return hr;
    }

    //  Initialize Capture Graph Builder by referencing pGraph (Graph Manager)
    hr = pGraphBuilder->SetFiltergraph(pGraph);
    if(FAILED(hr)){
        pGraphBuilder->Release();
        return hr;
    }

    //  Set pointer to Media Control Interface
    hr = pGraph->QueryInterface(IID_PPV_ARGS(&pControl));
    if(FAILED(hr)){
        return hr;
    }

    //  Set pointer to Media Event Interface
    hr = pGraph->QueryInterface(IID_PPV_ARGS(&pEvent));
    if(FAILED(hr)){
        return hr;
    }

    //  Create Sample Grabber
    //  NOTE: ISampleGrabber is depreciated and may not be supported in later versions of Windows!
    hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pGrabberF));
    if(FAILED(hr)){
        return hr;
    }

    //  Create the null renderer filter.  We don't be previewing the camera feed so we can just drop the frames when we've converted them to bitmaps
    hr = CoCreateInstance(CLSID_NullRenderer, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pNullF));
    if(FAILED(hr)){
        return hr;
    }

    TRACE(_T("Interface Creation Successful\n"));
    return S_OK;
    }

    //  Function to find the MS HD3000 webcam (VID=0x045E PID=0x0779)
    //  For more info on finding devices for Video/Audio capture, see https://msdn.microsoft.com/en-us/library/windows/desktop/dd377566(v=vs.85).aspx
    HRESULT webcamCapture::findWebCam(void){

    HRESULT hr;
    ICreateDevEnum *pDevEnum;
    IEnumMoniker *pEnum;
    IMoniker *pMoniker;
    BOOL isDeviceFound = FALSE;

    WORD wNumCameras = 0;

    hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pDevEnum));
    if(FAILED(hr)){
        return hr;
    }

    hr = pDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pEnum, 0);
    if(hr == S_FALSE){
        return VFW_E_NOT_FOUND;
    }

    pDevEnum->Release();

    //  Go through each device moniker and read their Device Path properties.  This is how we will find our webcam of interest
    while(pEnum->Next(1, &pMoniker, NULL) == S_OK){

        IPropertyBag *pPropBag;
        VARIANT var;

        hr = pMoniker->BindToStorage(0, 0, IID_PPV_ARGS(&pPropBag));

        if(FAILED(hr)){
            pMoniker->Release();
            continue;
        }

        VariantInit(&var);

        hr = pPropBag->Read(L"DevicePath", &var, 0);
        if(SUCCEEDED(hr)){
            //  String search variables
            CString csVidToCompare = _T("");
            CString csPidToCompare = _T("");
            WORD wVidSearchIndex = 0;
            WORD wPidSearchIndex = 0;

            CString csDevPath = var.bstrVal;
            csDevPath.MakeLower();

            wVidSearchIndex = csDevPath.Find(_T("vid_"), 0);
            wPidSearchIndex = csDevPath.Find(_T("pid_"), 0);

            csVidToCompare = csDevPath.Mid(wVidSearchIndex + 4, 4);
            csPidToCompare = csDevPath.Mid(wPidSearchIndex + 4, 4);

            //  If MS Device is found
            if(!csVidToCompare.Compare(_T("045e"))){
                //  If the 3000HD camera is found
                if((!csPidToCompare.Compare(_T("0779"))) && (wNumCameras == 0)){
                    wNumCameras++;
                    hr = pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pCapF);
                    if(FAILED(hr)){
                        return hr;
                    }

                    isDeviceFound = TRUE;
                    //  Add the webcam to the filter graph
                    hr = pGraph->AddFilter(pCapF, L"Capture Filter");

                    if(FAILED(hr)){
                        TRACE(_T("Failed to add webcam to filter graph\n"));
                        return hr;
                    }

                    TRACE(_T("Webcam found and added to filter!\n"));

                }

                else if((!csPidToCompare.Compare(_T("0779"))) && (wNumCameras > 0)){
                    TRACE(_T("More than one HD3000 camera found!\n"));
                    continue;
                }

                else{
                    TRACE(_T("MS Device found, but not the camera\n"));
                    continue;
                }
            }
        }

        pPropBag->Release();
        pMoniker->Release();
    }

    if(isDeviceFound == FALSE){
        TRACE(_T("Webcam was not found\n"));
        pEnum->Release();
        return E_FAIL;
    }

    pEnum->Release();

    return S_OK;
}

Answer 1

代码是正确的。是的，您可以像这样构建一个图形，单次拍摄模式下的样本采集器接受视频帧并指示完成。

潜在问题 list 包括:

1. 您的视频设备不提供帧，采样器将永远等待
2. 您请求转换为 24 位 RGB，并且您的相机更可能支持其他视频格式，因此您可能为您插入了另一个转换器过滤器 - 视频帧可能会离开相机过滤器并在转换器中丢失；您有兴趣查看您构建的有效图表
3. 你构建的图表不正确，你的样本采集器实际上没有正确连接

在任何情况下，您要做的第一件事就是简单地进入调试器并检查线程，您可能会当场发现错误。那么你要做的第二件事就是找出如何review your filter graphs .这是任何 DirectShow 开发所必需的。

S_FALSE 返回对于在拓扑中具有实时源的图是典型的。这很好。