mencoder is a package that allows you to convert files from one video format to another - there’s currently no GUI for it in Ubuntu.  You can convert it to other types and add a whole bunch of options, but we’ll just focus on this.  

1) Get mencoder.

sudo apt-get install mencoder

2) Move the files to the directory.

3) cd (change directory) into the directory where the files are.

4) Convert:

mencoder -idx test.ogg -ovc lavc -oac mp3lame -o test.avi