Split screen effect

Dear All, I would like to progressively split the screen in my movie, I mean to get the split bar to move slowly from left to right with the second screen to progress slowly. I have plenty of split screen effect, but it's always static, you get the split once for all, or not at aln. The only plug ins I found is the Tokyo split animator where you can set more or less the transition speed, but it's difficult to set up, it depens of the length of the clip. I would like to discover slowly my second screen coming from the left to the right. Any thoughts how to do this ? Thanks

Keyframe the Crop properties?

I'd also recommend key-framing the crop/position etc. properties. But if it's something your doing a lot or may want to retime/reposition until you get a nice feel I have an effect called "Split Screen Builder" on my "Template Master App" that makes it a lot quicker and easier, check the App Store.