Action Menu Audio Converter is a very simple frontend for ffmpeg, that has to be started directly by file manager.

It can be used in KDE desktop (Dolphin, Konqueror), MATE (Caja), LXDE (PCManFm) and LXQT(PCManFm-Qt).
MATE users must install caja-actions to make it works.
There is no particular desktop dependencies, so it could be possible to make it usable with other desktops (XFCE, CINNAMON...not sure for GNOME).

Then, when you right click on an audio file in your file manager, you will see actions->convert to format->(OGG, FLAC, MP3, WAV).

In case of video files, it will be actions->extract audio to format->(OGG, FLAC, MP3, WAV).
On right click on folders, it will be actions->Convert audio files to format->(OGG, FLAC, MP3, WAV).

It can converts audio files or extract audio from video file to wav, flac, ogg or mp3.
User can only change samplerate and quality (Bit depth in case of wav and flac formats).