First web video editor, using web codecs. This video editor does not use server only client resources. It is very fast compared to ffmpeg wasm for coding tasks.
Demuxer mp4 https://github.com/gpac/mp4box.js
Demuxer webm -> This link does not have a cdn https://github.com/jscodec/jswebm
Multiplexor mp4 https://github.com/Vanilagy/mp4-muxer
Multiplexor webm https://github.com/Vanilagy/webm-muxer
I am working here on a valid demo, I am currently making the script compatible in the browser environment and in the worker environment so that I can use it in both ways. https://tiuvi.com/videoEditorWebCodecs
You can investigate the files directly in sources, videoStreamWorker.js is the main one to edit the video file