movie maker

I'm a new independent app developer, and I've made an app called Live Canvas. It'll stick your Live Photos together into movies, convert a live photo to a gif, and also export a still frame. All options make it easy to share them to any service or device. The idea for this came from my nephew...

TL;DR I can't get iMovie, so I need an alternative (that is free and 10.7.5 compatible). Any suggestions? Operative word being free. It doesn't have to be the best, I just need something where I can upload a video, put a song in the background and play the video on fast foward while the song...