Actually I have such an app that I downloaded some time ago. It allows you to play a music track and tap out the beat and find how many frames between beats. For analyzing vocal tracks I use Papagayo which is a free track analyzer. And I recently installed Storyboarder (also free) which you can draw storyboards in your computer and output the frames in various formats including animated gif.
Let me dig up the metronome app and a way to upload it and the links for Papagayo and Storyboarder.