Some music and video formats are not supported by Linux immediately after installation because they depend on software that is either not open source or not free. In fact, it is technically illegal to watch DVDs because the required software is not licensed for use
on Linux.

Still, no-one appears to have been prosecuted for this yet and Ubuntu has collected all of this software together into one update. Left-click on the Applications menu and then on Add/Remove.

You will need to enter your password to continue. Make sure the Add/Remove utility is set to show all available applications, type restricted extras into the search box and press enter.

Click on the box next to the entry ubuntu-restricted-extras and then left-click on Mark for installation. Left-click on the Apply button and Ubuntu will download and install the media software.

This also includes Flash and Quicktime, which are often used on websites. Youtube uses Flash video for example.