This is an X11 based GUI for the libxine video player library. It provides xine, a skin based media player that can play all the audio/video formats that libxine supports. Currently, this includes MPEG1/2, some AVI and Quicktime files, some network streaming methods and disc based media (VCD, SVCD, DVD). A more complete list can be found on http://xinehq.de/index.php/features/.
Most DVDs on the market today are play-protected by the Content Scrambling System (CSS). Xine does not provide any code to descramble those DVDs, because of legal uncertainties. Have a look at /usr/share/doc/xine-ui/README.Debian for more information!