Follow these steps to play most common multimedia formats, including MP3, DVD, Flash, Quicktime, WMA and WMV, including both standalone files and content embedded in web pages.
Ubuntu 7.10, 8.04, and 8.10
Go to Applications → Add/Remove…
Set Show: to All available applications
Search for ubuntu-restricted-extras and install it. Note that there is also xubuntu-restricted-extras (for Xubuntu) and kubuntu-restricted-extras (for Kubuntu.)
Or open the Terminal, and execute the following command:
sudo apt-get install ubuntu-restricted-extras