Use mplayer and/or xine.
Visit Dag Wieers site and download install both the yum and rpmforge-release packages as per the instructions found here (yes yum does work for RHEL for third party stuff);
http://dag.wieers.com/home-made/apt/FAQ.php#B
Then it is as easy as; yum -y install mplayer xine
And you might want to get some additional mplayer codecs installed;
http://www.mplayerhq.hu/design7/dload.html
Scroll down and get the codecs (Linux x86 20061022) they go in a directory called;
/usr/lib/codecs