Here's a gui I put together for ffmpeg supported file types (video, audio, and images).
You will need yad and ffmpeg installed to use this. Depending on the type of file you open with yff you'll have a different gui with various conversion and extraction options.
This is basically a yad version of code from my gtkdialog programs ffvid, ffaudio, and ffpic.
0.4 - minor tweaks
0.5 - bugfixes
0.6 - added the ability to split audio file on chapter marks and some more bugfixes
0.7 - added audio option to downmix with amix filter and ability to concatenate audio files
0.8 - added more audio and video options
0.9 - added an explanation of what the program can do when opening from the menu
1.0 - Improved some code thanks to @step
1.1 - minor updates
1.2 - bugfixes
1.3 - added a cut+concatenate (cut multiple portions of video and join them together, eliminating unwanted sections of video) option for videos at request of @smokey01
1.4 - added some improvements in the image conversion portion of the script and a bugfix
1.5 - modified code to use a yad tail viewer instead of a terminal pop up
1.6 - bugfix for concatenating files
1.7 - bugfixes, added more options, simplified others
1.8 - removed the gtk buttons, simplified the drag and drop screen and added an information button to display all the extra information
1.9 - cleaned up some code