I want to create this effect using expressions.
I made this using keyframes, but it's pretty laborious.

link to vid: https://dl.dropbox.com/u/43613152/test.mp4

It would be cool if I could let the beat of a song control the reveal, thats what i'd really like.

I've been looking all over for the syntax to create masks but I can't find it.

I want to create a transition where your video transitions into another by being masked out slice by slice and the slices are all different widths.

Frank