I’ve been using the ffmpeg wasm library directly for a couple of years now and it’s working OK in production though it has a number of critical issues that don’t show up except in heavy testing with a wide variety of inputs and outputs.

Note that a lot of the ffmpeg code is not memory safe and some of the file/codec plugins contain memory errors. An out-of-bounds read or write will bring down the entire wasm subsystem (and does). You have to manually figure out which codecs are actually safe to use in the browser, vs which ones are merely exposed by the ffmpeg wasm builds.