Great work on this - I made a terminal command similar to this (llmpeg), and was actively trying to get exactly this working - a webasm compiled version of ffmpeg that could encode in the browser. I for the life of me couldn't get the provided examples on https://github.com/ffmpegwasm/ffmpeg.wasm to run.
Just for my own development curiosity, was there anything specific you had to do to get ffmpegwasm to work?