The Free Multimedia Framework GStreamer is a streaming-media framework, based on graphs of filters which operate on media data. Applications using this library can do anything from real-time sound processing to playing videos, and just about anything else that is media-related.

Kaffeine is a Free KDE Media Player that is good at handling various types of media. You can use it to play most of the media and has a nice support for many types of codecs. Kaffeine uses the Xine as an engine and it tries to make the most of it.