Associate custom thumbnail with Video

Superhive3

Hi.

I am seeking a method to associate a custom-sized thumbnail with a video.

I have figured out how to call the default Video thumbnail, but there is a restriction where the thumbnail needs to match the size of the video. I am looking for a way to have a thumbnail that is, for example, three times the pixels wide as tall (while the video is 640 x 324)

Any thoughts on ways to associate (perhaps by tag?) a thumbnail with a video. I'm at a loss, but sure would like to use SMugMug as the backbone for this simple app.

Thanks

x