Although there's been no shortage of iPhone DJ apps in the past few years, they've remained fairly niche, since Apple didn't allow devs official access to the iPod music library -- mobile DJs needed to upload a second separate music library per app, and that's no fun at all. Looks like that's about to change, though: one of the 1500 new APIs in iOS 4 provides direct access to the iPod library, meaning music apps of all kinds can play your tracks in any wacky way they want -- including, yes, scratching them. The first app to support the new API in the store is Flare Scratch, which is a relatively simple scratch app -- we just gave it a shot and yes, it does indeed load tracks from the iPod library and let you scratch 'em. There's a bit of a wait when loading up a new track, though, so it's not totally fluid to use in anything but a hey-this-is-fun context, but we're betting we'll see more serious DJ apps hit with smoother transitions soon enough -- and we can't wait to see what devs do once iOS 4 hits the iPad and they've got more room to work with. Video after the break.