It's a Matrox M-series. I'm not at the windows machine right now.
But one clue is, that jit.window shows only the topmost pixel of the file but it is stretched all the way down the screen. If I set the @noaccel 1, it works. This apparently disables opengl acceleration. When I put the video stream into the jit.gl.videoplane and use jit.gl.render to render the image to the jit.window it again only shows the topmost pixel. This time @noaccel 1 in the jit.window has no effect. Probably, because we are now in the opengl world, right?
I have downloaded the latest driver for the graphics card.