[Zubersoft]

Technically, MobileSheets will accept .mp3, .mp4, .m4a, .aac, .flac, .ogg, .mkv, .3gp, .ts, .mid, .xmf, .msmf, .rtttl, .rtx, .ota, .imy, .wav and .wma, but that is only Android (the support differs a little per OS depending on what the Audio framework on that OS supports). I generally would recommend sticking with the most common file formats, and you will have the least number of issues if you use mp3.

Mike