rm is real media file. http://en.wikipedia.org/wiki/RealMedia

mpg is mpeg which can be anything from mpeg 1-4 (there's many more but they're not on the market yet) http://en.wikipedia.org/wiki/Mpeg / http://abma.x-maru.org/faq/annotated/formats.mpg.php

avi = Audio Video Interleave. It is a special case of the RIFF (Resource Interchange File Format). AVI is defined by Microsoft. AVI is the most common format for audio/video data on the PC. AVI is an example of a de facto (by fact) standard. http://en.wikipedia.org/wiki/AVI


We normally recommend VLC - (click on link) _ (choose nearest mirror site) as it is a free player with in-built codecs & can play most files except realmedia files.

BTW MPlayer is very similar to VLC but it can play RM files. There's one or 2 things the other player can't do compared to each other.

Well if I'm that slow at replying I'm going to bed!!! lol