Twitch is typically 6Mbps+ and 1080p, though with more time to encode you can get the same quality out of fewer bits. Netflix can go up to about 20Mbps for 4K if my searches can be believed, but I didn't test it myself. When I've grabbed videos off Nebula they're a lot bigger than youtube; one here that doesn't even have much motion is 4Mbps at 1080p. And crunchyroll has a lot of 8Mbps at 1080p.

But acceptable quality can definitely go smaller. Especially if "acceptable" is judged by the significant compression artifacts I see on actual cable TV all the time.