If the license is under CC-BY-3.0, then based on the Creative Commons website, you can adapt and remix it, which includes changing the file format. You will have to still give attribution for the music, and I wouldn't recommend redistributing the file directly, though using it in a game should be fine.
That said, the license that the music comes under may be CC-BY-3.0 with custom additions and restrictions, rather than the straight CC-BY-3.0 license. I would look at the file and see if it says anything about restrictions on "adapting" or "remixing", or even better "formatting", just to make sure there isn't anything custom there.
Disclaimer: I'm not a lawyer or anything! Please take what I have written with a grain of salt.
