Yeah but playing a movie is a lot harder than displaying a bunch of pictures in quick succession. First of all, the script would require an outside library to actually decode the video file since Ruby would be far too slow to actually do it on it's own. Then you have to worry about trying to pass each frame from the library to the RGSS engine. Since the library can't just decode it and automatically convert it to a ruby bitmap, you'd have to write your own conversion process for that. And if you don't want to do that, the other route I could think of is having the outside library render on top of the RGSS window using a window handler. But the problem arises when the video would get rendered on top and not behind like you would want. See how complicated this would be?
I'm not trying to be a dick or anything, but this is a lot of work for a scripter to do. Your best bet is to use the Picture Movie add-on from ToA and use 400+ images. I'm not being mean, but no ones probably going to fulfill this request.