使用DirectShow预览时无法捕获摄像机视频源

#include <dshow.h>
#pragma comment(lib, "strmiids.lib")

int main() {
    IGraphBuilder *pGraph = NULL;
    ICaptureGraphBuilder2 *pBuild = NULL;
    IMediaControl *pControl = NULL;
    IMediaEvent   *pEvent = NULL;

    // Initialize the COM library.
    HRESULT hr = CoInitialize(NULL);
    if (FAILED(hr)) {
        printf("ERROR - Could not initialize COM library");
        return -1;
    }

    // Create the Filter Graph Manager and QueryInterface for IMediaControl and IMediaEvent.
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, 
                        IID_IGraphBuilder, (void **)&pGraph);
    if (FAILED(hr)) {
        printf("ERROR - Could not create the Filter Graph Manager.");
        return -1;
    }

    hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);

    // Create the Capture Graph Builder.
    hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, CLSCTX_INPROC_SERVER, 
                        IID_ICaptureGraphBuilder2, (void **)&pBuild);
    if (FAILED(hr)) {
        printf("ERROR - Could not create the Capture Graph Builder.");
        return -1;
    }

    // Set the Filter Graph Manager.
    hr = pBuild->SetFiltergraph(pGraph);

    // Render the video capture pin.
    hr = pBuild->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, NULL, NULL, NULL);
    if (FAILED(hr)) {
        printf("ERROR - Could not render the video capture pin.");
        return -1;
    }

    // Run the graph.
    hr = pControl->Run();
    if (FAILED(hr)) {
        printf("ERROR - Could not run the graph.");
        return -1;
    }

    // Wait for completion.
    long evCode;
    pEvent->WaitForCompletion(INFINITE, &evCode);

    // Clean up.
    pControl->Stop();
    pEvent->Release();
    pControl->Release();
    pBuild->Release();
    pGraph->Release();

    CoUninitialize();
    return 0;
}