There's no extra back and forth. You have to fetch the songs from the datacenter in the first place, right? So you fetch the additional data at the same time.

There's no extra back and forth. You have to fetch the songs from the datacenter in the first place, right? So you fetch the additional data at the same time. If Apple wanted to support this for user-provided mp3s then on-device would make sense. It doesn't sound like they support that though.