For ergonomics, the plugin should be able to spot cuts in the video so you can easily select the correct frames.
This shouldn't even be too hard, I doubt YouTube is completely rerendering every video with ads, they'd just insert the ad in before an I frame in the video. So each ad will start with an I frame, and the video will resume on an I frame, meaning just let the user select all the I frames, no fancy cut detection algorithm is needed.
I have no idea how to do this from JS though.
Also I mean video I frames, not HTML iframes.


The unflipped version was also shared yesterday, for those who missed it: https://fedia.io/m/lemmyshitpost@lemmy.world/t/1017044