Curlew is an easy to use, Free and Open-Source Multimedia converter for Linux.
MystiQ
Easy to use and elegant Multimedia converter.
Sound Konverter
soundKonverter is a frontend to various audio converters.
DeaDBeeF
DeaDBeeF sinit te ludere varietatem formarum audio, inter eas converti, UI more quovis fere modo vis, et multis additis plugins utere quae etiam plus extendere possunt.
Ciano
The ciano is a multimedia converter for all the format you need.