The problem with with this approach is that you're only considering time to first byte, which is part of the equation especially in the case of smaller files like scripts, but in case of larger files like video segments, throughput is more important. If you only wait for 1kB to download, then you essentially measure time to first byte.

Then the instruction to stop the download is not instantaneous, so by the time you realize you have downloaded 1kB on the client side, the server might already have sent the whole video segment on the other side, so this is not the way to go in order to optimize congestion

You should take a look at WebRTC's DataChannel. We're using it at Streamroot to do P2P video streaming in the browser.

You're talking about filesharing in P2P, again, totally something you can do with WebRTC. You should take a look at PeerJS if you want to experiment in no time.

You also talked about BitTorrent in the browser: you should definitely take a look at WebTorrent

You'd spot that right away if you had a visual jshint/jslint plugin in your IDE. It's a real time saver to have one: there are dozens of cases like your example that are valid JS, although it's not what you intended to write.

Well probably because that's a very creative way to spread their marketing message. And because it is very well done technically as well: stitching video segments in an order that depends on user action, without any visible transition, means they put a lot of work on that.

So I don't think general UX/video guidelines apply in this case, even if they're valid for most cases for online video.

Sure, they should probably have used an adaptive bitrate video for users with poor connection, because here they can't pause and let the video prebuffer for a while. Other than that this is pretty impressive