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Enumerating Video Capture Devices

This topic describes how to enumerate the video capture devices on the user's system, and how create an instance of a device.

To enumerate the video capture devices on the system, do the following:

  1. Call MFCreateAttributes to create an attribute store. This function receives an IMFAttributes pointer.
  2. Call IMFAttributes::SetGUID to set the MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE attribute. Set the attribute value to MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_GUID.
  3. Call MFEnumDeviceSources. This function receives an array of IMFActivate pointers and the array size. Each pointer represents a distinct video capture device.

To create an instance of a capture device:

The following code shows these steps:


HRESULT CreateVideoDeviceSource(IMFMediaSource **ppSource)
{
    *ppSource = NULL;

    IMFMediaSource *pSource = NULL;
    IMFAttributes *pAttributes = NULL;
    IMFActivate **ppDevices = NULL;

    // Create an attribute store to specify the enumeration parameters.
    HRESULT hr = MFCreateAttributes(&pAttributes, 1);
    if (FAILED(hr))
    {
        goto done;
    }

    // Source type: video capture devices
    hr = pAttributes->SetGUID(
        MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE, 
        MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_GUID
        );
    if (FAILED(hr))
    {
        goto done;
    }

    // Enumerate devices.
    UINT32 count;
    hr = MFEnumDeviceSources(pAttributes, &ppDevices, &count);
    if (FAILED(hr))
    {
        goto done;
    }

    if (count == 0)
    {
        hr = E_FAIL;
        goto done;
    }

    // Create the media source object.
    hr = ppDevices[0]->ActivateObject(IID_PPV_ARGS(&pSource));
    if (FAILED(hr))
    {
        goto done;
    }

    *ppSource = pSource;
    (*ppSource)->AddRef();

done:
    SafeRelease(&pAttributes);

    for (DWORD i = 0; i < count; i++)
    {
        SafeRelease(&ppDevices[i]);
    }
    CoTaskMemFree(ppDevices);
    SafeRelease(&pSource);
    return hr;
}


After you create media source, release the interface pointers and free the memory for the array:


    SafeRelease(&pAttributes);

    for (DWORD i = 0; i < count; i++)
    {
        SafeRelease(&ppDevices[i]);
    }
    CoTaskMemFree(ppDevices);


Related topics

Video Capture

 

 

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