First of all enable 'multiverse repository'. To do it go to System > Administration > Software Sources. Now click on the leftside radio button of "Software restrictecd by copyright or legal issue ( multiverse)".
Now click on 'Close', click 'Reload' on message box. Reloading or downloading package information will be done within seconds.
Now open terminal (Applications → Accessories → Terminal) and run the command below:
sudo dpkg –configure -a
Type password and press 'Enter'
Run the command below on the same opend terminal. It will justify and upgrad any missing or pending package.
sudo apt-get -f install
wait to complete the process. Now type/ run the commands below one be one. Always wait to complete one command.
sudo apt-get –fix-missing installAt last run the final command in the same opened terminal. This is the main command which will instal 'Ubuntu restricted extras' on Ubuntu system.
sudo apt-get clean
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
sudo apt-get install ubuntu-restricted-extras
Wait until finishing the downloading. Now Restart your machine. You will find that "ubuntu restricted extras" has been installed succesfully.