[Q] A video editor that can manipulate FPS of segments of my videos topic

I have the OnePlus One and could not be happier. However, next week I'd like to shoot a video where just a part of it is slow motion. I've been told that this is not possible to do natively with the camera. So what I want is shoot the whole video in 120fps and then adjust the rest to normal 24fps and leave the slowmo part. Anyone know an app that will do this? Or maybe a webapp?