Below is a picture of Memex's implementation of it, blends right below the player.
It allows you to make a quick summary from the transcript(entire video or portions of it). Gets addictive when you get the taste of escaping a chatty youtuber that you hate having to bite through. AI also helps with making annotations, when you are free to make your own along with screenshots.
The only feature Memex doesn't have is a "Timeline marker" which can be used to drop flags/markers that you can get back to later, maybe when you are done watching the video without any interruptions. I hate having to pause between videos since I cannot multitask while making annotations. Assign a hotkey to dropping markers and you know where to look for when you get back to making notes. allows cohesive flow of thoughts without interruption watching.
Combine markers with AI summaries, it'll prolly do it for you.