Ubuntu: Converting video & audio files in Ubuntu

Converting video files using ffmpeg in Ubuntu

Converting .3GA to AVI:

ffmpeg -i in_file.3ga out_file.avi

Converting video files using avconv in Ubuntu

Install libav-tools:

sudo apt-get install libav-tools

Converting video .OGV to MP4:

avconv -i in_file.ogv output_file.mp4

(Note:
RecordMyDesktop records in  .OGV format
Some Celphone records in  .3GA format)