在DirectShow中使用ICapturegraphBuilder

Question

I am working on Direct Show samples, and have run into a problem. I want to multiplex video recievedfrom capture device to both preview and file, but do not know how.

The sample i use as base is playcap. In there, ICaptureGraphBuilder2 is used; in its documentation is function SetOutputFileName that presumably turns on file output.

In practive, though, file appears in the file system, but is always empty and is deleted when the application exits. I suspect wrong usage of the API on my part.

Here is the code i am using:

    HRESULT hr;
IBaseFilter *pSrcFilter=NULL;

// Get DirectShow interfaces
hr = GetInterfaces();
if (FAILED(hr))
{
    Msg(TEXT("Failed to get video interfaces!  hr=0x%x"), hr);
    return hr;
}

// Attach the filter graph to the capture graph
hr = g_pCapture->SetFiltergraph(g_pGraph);
if (FAILED(hr))
{
    Msg(TEXT("Failed to set capture filter graph!  hr=0x%x"), hr);
    return hr;
}

// Use the system device enumerator and class enumerator to find
// a video capture/preview device, such as a desktop USB video camera.
hr = FindCaptureDevice(&pSrcFilter);
if (FAILED(hr))
{
    // Don't display a message because FindCaptureDevice will handle it
    return hr;
}

// Add Capture filter to our graph.
hr = g_pGraph->AddFilter(pSrcFilter, L"Video Capture");
if (FAILED(hr))
{
    Msg(TEXT("Couldn't add the capture filter to the graph!  hr=0x%x\r\n\r\n") 
        TEXT("If you have a working video capture device, please make sure\r\n")
        TEXT("that it is connected and is not being used by another application.\r\n\r\n")
        TEXT("The sample will now close."), hr);
    pSrcFilter->Release();
    return hr;
}
IBaseFilter * pBaseFilter;
IFileSinkFilter  *pfSink;
// Attach the file writerto the capture graph
hr = g_pCapture->SetOutputFileName (&MEDIASUBTYPE_Avi,L"output.avi",&pBaseFilter,&pfSink);
if (FAILED(hr))
{
    Msg(TEXT("Failed to set capture filter graph!  hr=0x%x"), hr);
    return hr;
}
// Render the preview pin on the video capture filter
// Use this instead of g_pGraph->RenderFile
hr = g_pCapture->RenderStream (&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video,
                               pSrcFilter, NULL, NULL);
if (FAILED(hr))
{
    Msg(TEXT("Couldn't render the video capture stream.  hr=0x%x\r\n")
        TEXT("The capture device may already be in use by another application.\r\n\r\n")
        TEXT("The sample will now close."), hr);
    pSrcFilter->Release();
    return hr;
}
// Now that the filter has been added to the graph and we have
// rendered its stream, we can release this reference to the filter.
pSrcFilter->Release();

// Set video window style and position
hr = SetupVideoWindow();
if (FAILED(hr))
{
    Msg(TEXT("Couldn't initialize video window!  hr=0x%x"), hr);
    return hr;
}

// Add our graph to the running object table, which will allow
// the GraphEdit application to "spy" on our graph
hr = AddGraphToRot(g_pGraph, &g_dwGraphRegister);
if (FAILED(hr))
{
    Msg(TEXT("Failed to register filter graph with ROT!  hr=0x%x"), hr);
    g_dwGraphRegister = 0;
}
// Start previewing video data
hr = g_pMC->Run();
if (FAILED(hr))
{
    Msg(TEXT("Couldn't run the graph!  hr=0x%x"), hr);
    return hr;
}

// Remember current state
g_psCurrent = Running;

return S_OK;

How should i achieve functionality i want?

Answer 1

In above code you are passing NULL to RenderStream as last parameter.

At RenderStream msdn documentation

it is stated:

If the pSink parameter is NULL, the method tries to use a default renderer. For video it uses the Video Renderer, and for audio it uses the Audio Renderer (WaveOut) Filter.

On the same above link, please have a look at the code snippet:

pBuilder->SetOutputFileName(&MEDIASUBTYPE_Avi, L"C:\\Example.avi",
    &ppf, &pSink);
pBuilder->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video,
    pCaptureFilter, NULL, ppf);

You might want to look at AmCap also.