From VDR Wiki
Mplayer is a powerfull media player designed for Linux and other UNIX like systems. MPlayer allows for playing almost all formats, including windows media and QuickTime media using both native Codecs and Win32 codecs. the mplayer-plugin allows users to play streaming media inside mozilla based browsers, such as, mozilla, firefox and konqueror.
Even thought this player was originaly created for Linux and UNIX there is an unstable beta release for Windows.
As mplayer is licenced under GPL anyone can download and modify the source code for mplayer, this means that mplayer allways changes and new releases are often available for download. There are also third party software that uses mplayer, such as the plugger plugin for mozilla browsers, it allows for pleaying allmost all media files, displaying word documents, photoshop images and much more.