Reading the documentation for FFmpeg, it seems like FFmpeg can also be used to concatenate and overlay video and edit the audio, and supports captions and subtitles and many other functions too. It would seem that Editly supports the use of JSON5, and the use of JavaScript and HTML for custom graphics/animations (although I don't see a lot of the stuff that FFmpeg does in the documentation for Editly), but what I want is the ability to use PostScript for custom graphics and animations, rather than JavaScript. Although external graphics/animations are also helpful, but I think FFmpeg already does that anyways (and it also supports APNG, too, which is better than animated GIF, I think). However, neither FFmpeg nor Editly support farbfeld, as far as I can see.