Vine just added a new feature that lets you remix audio on the fly, which sounds pretty neat.
Now available on the iOS app, it adds an option 'Make an audio remix' in the menu. This will pull out the sound from the Vine you're currently watching and let you replace it with something live from your camera or even the sound from an existing video on your phone. It also looks like you can use this method to grab audio from another Vine and apply it to your video. Like so.
Given how incredibly creative the Vine community is, you can be sure this new option will result in all manner of crazy and inventive mixes. And also plenty of people robbing songs from popular vids in pursuit of those extra views. One interesting feature in that regard is the fact that you can find out the source of the original audio and remixes will be marked with a musical note in your feed.
This update is only on iOS for the moment.