使用DirectShow预览网络摄像头

在调用RenderStream（）时，我一直得到"E_INVALIDARG"。

我的程序输出是：

SUCCESS - Initialized COM library.
SUCCESS - Created the Filter Graph Manager.
SUCCESS - Created the Media Control and Media Event Interfaces.
SUCCESS - Enumerated devices.
--------------DEVICE INFORMATION--------------
Integrated Webcam
------------END DEVICE INFORMATION------------
SUCCESS - Bound to moniker.

这是代码：

#include "stdafx.h"
#include <dshow.h>      //direct show
#include <windows.h>    //windows
#pragma comment(lib,"Strmiids.lib") //used for direct show
HRESULT InitCaptureGraphBuilder(
    IGraphBuilder **ppGraph,  // Receives the pointer.
    ICaptureGraphBuilder2 **ppBuild  // Receives the pointer.
    )
{
    if (!ppGraph || !ppBuild)
    {
        return E_POINTER;
    }
    IGraphBuilder *pGraph = NULL;
    ICaptureGraphBuilder2 *pBuild = NULL;
    // Create the Capture Graph Builder.
    HRESULT hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, 
        CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2, (void**)&pBuild );
    if (SUCCEEDED(hr))
    {
        // Create the Filter Graph Manager.
        hr = CoCreateInstance(CLSID_FilterGraph, 0, CLSCTX_INPROC_SERVER,
            IID_IGraphBuilder, (void**)&pGraph);
        if (SUCCEEDED(hr))
        {
            // Initialize the Capture Graph Builder.
            pBuild->SetFiltergraph(pGraph);
            // Return both interface pointers to the caller.
            *ppBuild = pBuild;
            *ppGraph = pGraph; // The caller must release both interfaces.
            return S_OK;
        }
        else
        {
            pBuild->Release();
        }
    }
    return hr; // Failed
}
HRESULT EnumerateDevices(REFGUID category, IEnumMoniker **ppEnum)
{
    // Create the System Device Enumerator.
    ICreateDevEnum *pDevEnum;
    HRESULT hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL,  
        CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pDevEnum));
    if (SUCCEEDED(hr))
    {
        // Create an enumerator for the category.
        hr = pDevEnum->CreateClassEnumerator(category, ppEnum, 0);
        if (hr == S_FALSE)
        {
            hr = VFW_E_NOT_FOUND;  // The category is empty. Treat as an error.
        }
        pDevEnum->Release();
    }
    return hr;
}
void DisplayDeviceInformation(IEnumMoniker *pEnum, IMoniker** pMoniker)
{
    while (pEnum->Next(1, pMoniker, NULL) == S_OK)
    {
        IPropertyBag *pPropBag;
        HRESULT hr = (*pMoniker)->BindToStorage(0, 0, IID_PPV_ARGS(&pPropBag));
        if (FAILED(hr))
        {
            (*pMoniker)->Release();
            continue;  
        } 
        VARIANT var;
        VariantInit(&var);
        // Get description or friendly name.
        hr = pPropBag->Read(L"Description", &var, 0);
        if (FAILED(hr))
        {
            hr = pPropBag->Read(L"FriendlyName", &var, 0);
        }
        if (SUCCEEDED(hr))
        {
            printf("%Sn", var.bstrVal);
            if(0 == wcscmp(var.bstrVal, L"Integrated Webcam"))
            {
                VariantClear(&var); 
                pPropBag->Release();
                return;
            }
            VariantClear(&var); 
        }
        hr = pPropBag->Write(L"FriendlyName", &var);
        pPropBag->Release();
    }
}
void main()
{
    HRESULT hr = CoInitializeEx(NULL, COINIT_MULTITHREADED);
    IGraphBuilder *pGraph = NULL;
    ICaptureGraphBuilder2 *pBuild = NULL;
    IMediaControl *pControl = NULL;
    IMediaEvent   *pEvent = NULL;
    if (FAILED(hr))
    {
        printf("ERROR - Could not initialize COM libraryn");
        return;
    }
    printf("SUCCESS - Initialized COM library.n");
    hr = InitCaptureGraphBuilder(&pGraph, &pBuild);
    if (FAILED(hr))
    {
        printf("ERROR - Could not create the Filter Graph Manager.n");
        return;
    }
    printf("SUCCESS - Created the Filter Graph Manager.n");
    hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
    if (FAILED(hr))
    {
        printf("ERROR - Could not create the Media Control or Media Event Interfaces.n");
        return;
    }
    printf("SUCCESS - Created the Media Control and Media Event Interfaces.n");
    IEnumMoniker *pEnum;
    hr = EnumerateDevices(CLSID_VideoInputDeviceCategory, &pEnum);
    if(FAILED(hr))
    {
        printf("ERROR - Failed to enumerate devices.n");
        return;
    }
    printf("SUCCESS - Enumerated devices.n");
    IMoniker* pMoniker = NULL;
    printf("--------------DEVICE INFORMATION--------------n");
    DisplayDeviceInformation(pEnum, &pMoniker);
    printf("------------END DEVICE INFORMATION------------n");
    IBaseFilter *pCap = NULL;
    hr = pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pCap);
    if(FAILED(hr))
    {
        printf("ERROR - Failed to bind to moniker.n");
        return;
    }
    printf("SUCCESS - Bound to moniker.n");
    hr = pBuild->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video, pCap, NULL, NULL);
    if(FAILED(hr))
    {
        printf("ERROR - RenderStream() failed.n");
        return;
    }
    printf("SUCCESS - RenderStream() succeeded.n");
    hr = pControl->Run();
    if(FAILED(hr))
    {
        printf("ERROR - Run() failed.n");
        return;
    }
    printf("SUCCESS - Running.n");
    long evCode;
    hr = pEvent->WaitForCompletion(INFINITE, &evCode);
    if(FAILED(hr))
    {
        printf("ERROR - WaitForCompletion() failed.n");
        return;
    }
    hr = pControl->Stop();
    if(FAILED(hr))
    {
        printf("ERROR - Stop() failed.n");
        return;
    }
    printf("SUCCESS - Stopping.n");
    pControl->Release();
    pEvent->Release();
    pGraph->Release();
    pMoniker->Release();
    pEnum->Release();
    CoUninitialize();
}