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Step 2: Add a Menu Command to Grab a Poster Frame

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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 It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation.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.]

[This API is not supported and may be altered or unavailable in the future.]

This topic is Step 2 of Grabbing a Poster Frame.

Next, add a command for the user to grab a poster frame from a file. Create a menu item with a resource ID of IDM_BITMAP, and add the following case statement to the window procedure:

case WM_COMMAND:
    switch (LOWORD(wparam))
    {
    case IDM_BITMAP:
        {
            HRESULT hr = DoShowBitmap(hwnd, &pbmi);
            if (SUCCEEDED(hr))
            {
                pBuffer = reinterpret_cast<BYTE*>(pbmi) + 
                    sizeof(BITMAPINFOHEADER);
                InvalidateRect(hwnd, NULL, TRUE);
            }
            else
            {
                MessageBox(hwnd, TEXT("Cannot display the image."),
                    TEXT("Error"), MB_OK | MB_ICONERROR);
            }
        }
        break;  // IDM_BITMAP
    }
    break;  // WM_COMMAND

The DoShowBitmap function will return the allocated buffer in pbmi. Assuming the function succeeds, the address of the bitmap (

pBuffer

) can be calculated as an offset from pbmi. In the DoShowBitmap function, display an Open File dialog box for the user to choose a file, and then call the application-defined GetBitmap function, which will retrieve the bitmap:

HRESULT DoShowBitmap(HWND hwnd, BITMAPINFOHEADER** ppbmih)
{
    OPENFILENAME ofn;       // common dialog box structure
    // Initialize OPENFILENAME (not shown).
    // Display the Open File dialog box.  
    if (GetOpenFileName(&ofn) != TRUE) // failed to open file
    {
        return E_FAIL;
    }
    return GetBitmap(ofn.lpstrFile, ppbmih);
}

Next: Step 3: Implement the Frame-Grabbing Function

Grabbing a Poster Frame