ffmpeg is a cli alternative. From memory, handbrake uses that for the work performed.
Discussion
Interesting! I didn't know this.
I have a bunch of little scripts I've written that utilize ffmpeg, its perfect for building macros and things, especially when converting or editing entire folders of GIF or WEBP and the like. Didn't know Handbrake used that. Thats cool
ffmpeg is quite good at a bunch of esoteric things as well. Like time lapse speed up.