Mp3, Ogg, FLAC, etc are forms of audio compression. Those files are already compressed, so you're not going to get much more (if any) compression on them. Same goes for Jpegs, PNG, and TIFF (image compression formats); rar, tar, zip (general file compression) and most any other media format------unless you know that it's in a raw, uncompressed form (like a .wav).
The only thing we have to fear is a giant wheelchair-crushing squid. - Franklin D Roosevelt