[bjano]

You don't need to keep the video files in memory, it's enough to have the javascript File object and then you can read the packets you need on the fly. This way the app's memory usage should be okay.

This is what I did in my similar project (vidmix.app) and seems to be what OP's project is doing, except that they also copy the file to indexedDB to keep it around after the browser tab is closed.