smpeg is an mpeg decoding library, which runs on just about any platform. It comes with two sample decoders, plaympeg (console, no UI), and gtv, a simple GTK+ interface.

You can check out smpeg from Subversion via these simple instructions:

You can see the web-based svn interface here

You can subscribe to the mailing list for smpeg by sending a blank e-mail to: smpeg-subscribe@icculus.org