I checked out your script, though I'm a little confused as to how it works.  My background video is also saved as a series of BMP images (that's how I export), so I ran your script and took the first frame of the sequence under 'Get Background'.  I then clicked 'Make Animation', though it only rendered the first frame of animation.

If I want to, say, render a 180 frame animation with 180 background images (as opposed to an AVI), how would I go about doing that?

Thanks!