Anyway, thanks to the growing popularity of Linux, now anything that can be done in MS Windows can be achieved, even better, in Linux!. So, in that sense, if you're looking for an easy to use cross-platform video/audio converter for Ubuntu/Linux, then DamnVid is one of the best apps!.
It uses the FFmpeg library and not only for converting videos to various other formats, but can be used as a tool for downloading videos from various online sources as well.
*. Convert your videos and audios from one format to a whole dozens of other formats (mp3, Ogg vorbis, .avi, mpeg, H.264, H.263...)
*. Online video download-er.
*. Predefined "options" - such as one click to iPod or PSP for instance.
*. Easy to use GUI.
*. Convert files while they are being downloading!... are just a few to name.
So, if you use Ubuntu and wondering how to install DamnVid, then open your terminal and enter the below command (using a PPA channel).
sudo add-apt-repository ppa:damnvid/ppa
sudo apt-get update
sudo apt-get install damnvid