Various players can play m4a files. Off-hand, iTunes, QCD (after downlding a plug-in), winamp (need xtra plug-in for older versions), nero, roxio, etc. See
http://www.m4a.com/ & also
http://www.hydrogenaudio.org/forums/...hp/t30054.html &
http://www.analogduck.com/main/m4a