What app does Lawrence Young use?

Lawrence Young is famous for his Youtube videos. He cleverly uses an effect which splits the screen into multiple videos of him singing in harmony.

There is an app called Video Merger (https://itunes.apple.com/us/app/video-merger-free-combine/id880953154?mt=8) which sounds like it does something similar to what Lawrence is doing...

But in order to get the timings for his harmonies in sync so accurately, I wouldn't be surprized if he's using a software suite like iMovies.

Either way, the result is a really powerful and melodic rendition, and a kind of surreal visual effect where there are several Lawrence Youngs singing at the same time!

Check it out: