Install WinFF onto your Ubuntu installation. WinFF is a GUI (graphical user interface) front end for the FFmpeg conversion software. You can use the command line installation by opening a terminal window from the Applications > Accessories > Terminal menu and typing:
sudo apt-get install winff
You can also use the Synaptic Package Manager from the "System > Administration > Synaptic Package Manager" menu to install the software--search for the WinFF program, tick the check box and hit "Apply" to install the program and its dependencies.