Vorbis
From Mario Fan Games Galaxy Wiki
The OGG file format is a sound format that is similar to MP3 in the sense of quality and compression, though it loses a minimal amount of quality due to the sheer compression. A disadvantage of using this format is that it usually relies on external DLLs for playback. Because it has a high compression rate and a much better sound quality than MIDI, MFGGers have begun to use OGG music in their fangames.
Multimedia Fusion 2 supports OGG natively as opposed to MP3.