Curlew is an easy to use, Free and Open-Source Multimedia converter for Linux. It written in Python and GTK3 and it depends on FFmpeg or Libav.
Main features:

Easy to use and clean user interface.
Hide the advanced options with the ability to show them.
Convert to more than 100 different formats.
Allow to edit formats.
Shutdown or suspend PC afer a conversion process.
Show file informations (duration, remaining time, estimated size, progress value).
Show file details using mediainfo.
Allow to skip or remove file during conversion process.
Preview file before conversion.