Interesting to see this.

A couple months ago I launched a site (https://familymemorystream.com/) that allows annotating videos but is targeted towards the niche of converted family videos.

I was considering opening it up to make a generic "video note taker" version; it looks like you beat me to it :) Best wishes! It will be interesting to see where you end up with the pricing model. It looks like you're using YouTube/Vimeo for the video hosting so that frees you up to do one-time purchases if you want since your server costs will likely stay fairly constant across scale.