I use the GNOME video player that is installed by default in Ubuntu 9.04 – Jaunty Jackalope. Its name is Totem, and it can be either based on GStreamer or xine. I am using GStreamer as this is the default configuration.
Recently, I tried to watch a DVD on this player, but very soon I figured out that some codecs should be missing, because the DVD couldn’t be played. After searching a little on the internet, I came to the conclusion that this problem can be solved just writing a couple of line in the console:
$ sudo apt-get install gstreamer0.10-ffmpeg gstreamer0.10-plugins-ugly gstreamer0.10-plugins-ugly-multiverse gstreamer0.10-plugins-bad gstreamer0.10-plugins-bad-multiverse
$ sudo apt-get install libdvdcss2
And… this is all!