Step 1. Specify the Media Type

You must configure the Sample Grabber for the desired media type before you connect it to any other filters. First call CoCreateInstance to create the Sample Grabber, and IFilterGraph::AddFilter to add it to the filter graph. Then query the Sample Grabber for the ISampleGrabber interface and call the ISampleGrabber::SetMediaType method. This method specifies the media type that the Sample Grabber will use to connect. You can specify just the major type; or the major type plus the subtype; or the major type, subtype, and format type. (For more information, see AM_MEDIA_TYPE.)

For example, if you want to grab an uncompressed video frame that is compatible with the current display mode, set the major type to MEDIATYPE_Video and set the subtype based on the current bit depth of the display:

// Create the Sample Grabber.
IBaseFilter *pF = NULL;
ISampleGrabber *pGrabber = NULL;
hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER,
    IID_IBaseFilter, reinterpret_cast<void**>(&pF));
hr = pF->QueryInterface(IID_ISampleGrabber,
    reinterpret_cast<void**>(&pGrabber));
hr = pGraph->AddFilter(pF, L"SampleGrabber");
// Find the current bit depth.
HDC hdc = GetDC(NULL);
int iBitDepth = GetDeviceCaps(hdc, BITSPIXEL);
ReleaseDC(NULL, hdc);
// Set the media type.
AM_MEDIA_TYPE mt;
ZeroMemory(&mt, sizeof(AM_MEDIA_TYPE));
mt.majortype = MEDIATYPE_Video;
switch (iBitDepth)
{
case 8:
    mt.subtype = MEDIASUBTYPE_RGB8;
    break;
case 16:
    mt.subtype = MEDIASUBTYPE_RGB555;
    break;
case 24:
    mt.subtype = MEDIASUBTYPE_RGB24;
    break;
case 32:
    mt.subtype = MEDIASUBTYPE_RGB32;
    break;
default:
    return E_FAIL;
}
hr = pGrabber->SetMediaType(&mt);