It was more of a suggestion of a way to try solve the issue, since the more obvious way of scripting it would appear to be a little difficult. It wouldn't be too bad if you could see inside Graphics and see what that normally does to try to add something to it.
It's obvious from the description in the help file that videos especially aren't scaled down if they are bigger, thus implying that no algorithm exists in the coding for down or upscaling. You'd have to do this yourself.
The thing about scaling is that if you stretch it too much you end up with artefacts, unless you do some kind of upscaling before you apply the image. The same would be true of videos.
It may be possible using video processing ideas, but how much work it would take I have no idea. It may also limit the platforms that can play the game. Considering that videos are only cut when larger than the resolution and are played centrally in the window, as long as the resolution that a player chooses isn't less than the video resolution, and was maybe proportional to the video, it wouldn't look awful. A lot of old games used to have a set video resolution but had scaled images, probably because it was easier to render images in different resolutions than videos.