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Capturing Video to a Windows Media File

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[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

To capture video and encode it to a Windows Media Video (WMV) file, connect the capture pin to the WM ASF Writer filter, as shown in the following diagram.

windows media capture graph

The easiest way to build this graph is by specifing MEDIASUBTYPE_Asf in the ICaptureGraphBuilder2::SetOutputFileName method:

IBaseFilter* pASFWriter = 0;
hr = pBuild->SetOutputFileName(
    &MEDIASUBTYPE_Asf,   // Create a Windows Media file.
    L"C:\\VidCap.wmv",   // File name.
    &pASFWriter,         // Receives a pointer to the filter.
    NULL);  // Receives an IFileSinkFilter interface pointer (optional).

The value MEDIASUBTYPE_Asf tells the Capture Graph Builder to use the WM ASF Writer filter as the file sink. The Capture Graph Builder creates the filter, adds it to the graph, and calls IFileSinkFilter::SetFileName to set the name of the output file. It returns a pointer to the filter as an outgoing parameter (

pASFWriter

in the previous example).

Use the IConfigAsfWriter interface on the WM ASF Writer to set the Windows Media profile. You must do this before you connect any pins on the WM ASF Writer.

IConfigAsfWriter *pConfig = 0;
hr = pASFWriter->QueryInterface(IID_IConfigAsfWriter, (void**)&pConfig);
if (SUCCEEDED(hr))
{
     // Configure the ASF Writer filter.
    pConfig->Release();
}

For more information about setting the profile, see Creating ASF Files in DirectShow.

Call ICaptureGraphBuilder2::RenderStream to connect the capture filter to the ASF Writer:

hr = pBuild->RenderStream(
    &PIN_CATEGORY_CAPTURE,   // Capture pin.
    &MEDIATYPE_Video,        // Video. Use MEDIATYPE_Audio for audio.
    pCap,                    // Pointer to the capture filter. 
    0, 
    pASFWriter);             // Pointer to the sink filter (ASF Writer).

Each input pin on the WM ASF Writer filter corresponds to a stream in the Windows Media profile. You must connect every pin, so that the file content matches the profile.

Capturing Video to a File