> I would also love to inhabit the parallel universe where Netflix hands out a 4-minute buffer, because in this one 20 seconds seems to be on the high end.

Presumably it depends on the device, but I vaguely recall testing this out on a Chromecast, and I found Netflix to buffer up for several minutes. Some other streaming providers, such as Rakuten, only buffered around 15 seconds.

> I strongly suspect that Netflix's video and audio are sent in different streams

I think this might be right. They presumably want to support lots of different combinations of audio codecs and video codecs, so keeping them separate would make sense. Pure guesswork on my part though.