What iPhone app can I use to do this?

So I want to make videos like this;

which means I need an app I can use on my iPhone so speed up the video and add music from my playlist? I'd prefer a free app, but I don't mind paying a small amount.
If anyone could help I'd be grateful.

You can't. The best way to recreate a video like that is to make the video with your phone. Then you put that video onto your computer. There should be some video editing program to speed up videos, but I don't know any exact ones, so you might want to google search that, then you just make sure you have the music file on your computer and drag it into the video editing program. If your video editing program doesn't allow music to be added then just save the video as you have it speeding up then open it up in movie maker or iMovie