Gunstep is a new video series that uses Battlefield 4's gun noises and attempts to recreate Mario's music with them.
Actually, that might be a bit generous. It's more like the gunshots just punctuate the music but shiiii... it's still pretty cool!
It seems to be the first in a series. The second one, based on Zelda, is far, far rougher and not of the same quality, but just in case you're interested, you can check it out here.
Via Zelda Universe