c++ - 使用 DirectShow 预览网络摄像头

Question

我在调用 RenderStream() 时不断收到“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.

代码如下:

#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("%S\n", 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 library\n");
        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();
}

Answer 1

在使用 RenderStream 之前，您需要将相机过滤器IGraphBuilder::AddFilter 添加到图表中。