Comment by bastawhiz

If you visit the ffmpeg.wasm documentation, the first example on the Usage page does almost exactly this:

https://ffmpegwasm.netlify.app/docs/getting-started/usage

It transcodes a webm file to MP4, but making it speed up the video is trivial: just add arguments to `ffmpeg.exec()`. Your lack of success in this task is trusting an LLM to know about cutting-edge libraries and how to use them, not a lack of progress in the area.