HandBrake is an open-source, cross-platform multi-threaded video transcoder for Mac, Linux and Windows. You can use it to convert to and from different media formats. The availability of presets make the conversion easier even for novice users. Just select the media device to which you want the video to be transcode to and HandBrake will manage the rest.
HandBrake is not available in Ubuntu repositories yet. To install, you need to add a PPA of HandBrake releases. Type the following in terminal to install the latest version of HandBrake.
sudo add-apt-repository ppa:stebbins/handbrake-releases
sudo apt-get update
sudo apt-get install handbrake-gtk