Ubuntu – Does the optical drive not play commercial dvds

Another thing to check is that your region is set correctly on your DVD drive.
From Setting DVD Region Codes:

If your DVD player regularly locks up when you try to play back a DVD, your DVD player probably does not match the DVD's region code. Region codes are a form of vendor lock-in. For example, you cannot play a DVD published in Japan (Region 2) on a DVD player in the United States (Region 1) without changing the region code of the DVD player (unless you own a region-free DVD player). You can view or modify the region code of your DVD drive with the regionset tool.

You can install the regionset utility from universe with the following command:

 sudo apt-get install regionset

Then to set the region, insert a DVD from the region you want to use and run the following command (replace sr0 with the name of your DVD drive if different):

sudo regionset /dev/sr0

Note there is a 5 change limit (usually).
Also note most players will ignore the region set (and some drives come without any set region). Further details see Setting DVD Region Codes.

Open terminal (Ctrl + Alt + T) and run following command to install require dependencies :

sudo apt-get install gstreamer0.10-plugins-ugly gstreamer0.10-ffmpeg libxine1-ffmpeg gxine mencoder libdvdread4 totem-mozilla icedax tagtool easytag id3tool lame nautilus-script-audio-convert libmad0 mpg321 && sudo /usr/share/doc/libdvdread4/install-css.sh

Restart may necessary.

WARNING: Run encrypted video on Linux is illegal, so make sure its legal on your area.

See also:

• Why it is legal to play encrypted video on Linux ?

• Watching DVDs legal on USA

  UPDATE

Since medibuntu is no longer available, you have to install libdvdcss2 manually :

wget http://download.videolan.org/pub/debian/stable/libdvdcss2_1.2.13-0_i386.deb
sudo apt-get update
sudo dpkg -i libdvdcss2_1.2.13-0_i386.deb

Now encrypted dvd should run perfectly fine