It all depends on the particular player. Mine will recognize and play CDA, WMA, WAV, MP3, and maybe a couple of others that I haven't tried yet. CD-R is not a problem, I have not tried CD-RW as those are known to cause problems, even with some computers (that they were not written on). Unclosed sessions will not work. Multi-session most likely won't work for one of the sessions. A relatively up-to-date CD player "should" be able to play MP3's.