how to make AVI animation control transparent?


How can I make a AVI-animation control transparent?

I create by using:

CreateWindowEx(0, (LPSTR(ANIMATE_CLASS)), nil,
   $50000000 or dwStyle, x, y, nWidth, nHeight,
    hwndP, 0, hinstance, nil);
I tried ws_ex_transparent as dwStyle but the background is white then!

are all parameters correct? (I ask because that's not documented
in Win32 Help)

Thanks in advance for your help!