As a video editor (not professionally...just a hobbyist) anything to do with ffmpeg. Fast and easy to batch convert codecs, etc... Pretty much every function of most FOSS editors are built around ffmpeg, and nearly every function has a CLI equivalent. I mean, yeah, of course for a lot of those you have to have the GUI to see what you're doing. But there's plenty that can be done without even needing to open up your editor.