Not only is there an app for that, but it was featured in an apple commercial long ago. There's even a free version now that works just fine. You can even play you own playlist with it and it will look up the lyrics for you, which is a good cure for commonmislyriccossis. I'm sure by now you want me to stop jibbering and give you the name of said app... Ok then. Fine. Here it is. It's called SoundHound. Aaaand, can be found here, linky linky; https://itunes.apple.com/ca/app/soundhound/id355554941?mt=8