Updated August 3rd, 2005.
In addition to being completely free, Aniplayer is the most supported media player for GEM computers. It features modes to suck out the most performance for playing videos and supports many types, that, were simply not supported on linux until well after Aniplayer supported them. Didier Mequignon is the creator of this excellent media player and has worked almost singlehandedly from my understanding coding the efficient codecs. Aniplay is a proper gem application and works even under emulation or across any operating systems for Atari. It supports audio formats such as mpeg, ogg vorbis, real audio, avr, wave, etc. It supports most major video formats including divx, assuming your computer has the horsepower to play divx (most don’t). The unfortunate side effect to the efficiency of this program is that it only works on a 68030 based machine or higher (possibly 68020)… UPDATE: Though I originally wrote this, I’m not certain this is true as I remember at one time playing wave files on my STe with Aniplayer. Other features it includes are advanced playlist features allowing it to be a suitable replacement for any mpeg audio player you might currently be using. Little features here and there combined with an efficient foundation as well as proper gem programming make this media player perfect. A great example of how GEM software can and should be.
Related Link: Aniplayer Home Page