There is an ARM port of Windows - Windows Mobile, complete with codecs.

http://www.4winmobile.com/forums/pho...decs-here.html

(you must register to get the zip linked in the message) which contains wma[asv]dmod.dll (audio, speech, video), for ARM.

The DLL connection AFAIK is the same as windows, so an ARM port of the Wine DLL loader (used by mplayer for the ia32 codecs) should work, but I don't do windows so don't know the API. Worse, it doesn't seem to be a routine but some kind of codec object with callbacks and other stuff so it wouldn't be a matter of finding a decode function.