As far as I remember, the last working version of MPlayer for X5000 is version 1.1. Can be found here:

http://fabportnawak.free.fr/mplayer/

Version 1.4 on MorphOS-Storage is only with Altivec, which does not work on X5000:
"a seperate non-AltiVec version might be released at a later point" which never happened.

By the way, OS4 users can use the latest version 1.5:
https://os4depot.net/?function=showfile&file=video/play/mplayer.lha

Some time ago, I have asked the MorphOS developers also to release a non-Altivec version but unfortunately X5000 users are a minority so it was not worth the efforts...