Curlew Multimedia Converter is a free, open-source, and easy-to-use Multimedia converter for Linux. It depends on FFmpeg/avconv and is written in Python and GTK3.
Think of Curlew as a front-end to the renowned FFmpeg CLI-based media converter with a host of use options including hiding/showing advanced options, setting bit rates and output formats, using drag and drop to add selected files for conversion, e.t.c.