Hi Rick H,
The B2 will play WAV, FLAC, MP3, AAC and ALAC (Apple) files - ALAC files have a .m4a extension (but are shown as AAC on the B2).
AFAIK MPEG-4 is a video format that is not supported - have you transferred these to the B2 before?
The B2 will not compress or convert any files that are already compressed e.g. FLAC or MP3 or MPEG-4 (in your case).
Paul
Brennan Support.