That's true, but my understanding is they serve a specific mux for a specific bandwidth profile, and serve it by just transmitting bytes, no demux required. I d

That's true, but my understanding is they serve a specific mux for a specific bandwidth profile, and serve it by just transmitting bytes, no demux required. I didn't mean to imply that wasn't a common option. I only meant to say I don't think a common option is to have a giant mux of all possible bandwidth profiles into one container file, that has to be demuxed at serve time. My understanding is that YouTube supports both the "separate streams" and "specific mux per-bandwidth profile" methods, and picks one based on the codec support/preferences of the client.