Yes I 've red that it's not possible to play video on specific part ( that's a pity )
I just want to play a video on cutscene, at the correct original size. For now, if I play a 400x400 video on a 1024*768 game resolution for example, the video is streched to full screen, even if I do not check the fullscreen option.
So that's why I had idea to tweak with Aafter effects...Yes it seems that the black background is inevitable. But it can be better than strech a small video to fullscreen.
But as there is a ''if check'' box, with no effect, maybe it's a bug?