FFmpeg is a wonderful library for creating video applications or even general purpose utilities. ffmpeg takes care of all the hard work of video processing by doing all the decoding, encoding, muxing and demuxing for you. This can make media applications much simpler to write. It's simple, written in C, fast, and can decode almost any codec you'll find in use today, as well as encode several other formats.
WinFF is a GUI for the command line video converter, FFmpeg. It will convert most any video file that FFmpeg will convert. WinFF does multiple files (batch) in multiple formats at one time. You can for example convert mpeg's, flv's, and mov's, all into avi's all at once. WinFF is available for Windows, Debian, Ubuntu, Redhat based GNU/Linux distributions.
The installation of WinFF is very simple, just open the terminal and run the following command to install it.
sudo apt-get install winffOnce the installation is over, you can launch it from Applications > Sound &Video > Video Convert WinFF.
WinFF UI is really very simple to use, Click the Add button, to add the video which you wish to convert, then choose the destination file type from the Convert To drop down box. You can specify the destination folder to save the converted file by using the Output Folder option. The Additional Options section at the bottom of the window lets you specify the Video Bitrate , FrameRate and other relevant settings. Once done with all the settings hit the Convert button to convert the file.
If you want to use command line (ffmpeg) to convert Audio/Video - check here