Thanks, that makes sense!

It's interesting that it's very much an interactive experience for the end-user. But for the logic of the computer, it's not interactive at all.

You can make the contrast even stronger: if both video streams are transmitted over UDP, you don't even need to sent ACKs etc. To be truly one-directional from a technical point of view.

Then compare that to transferring a file via TCP. For the user this is as one-directional and non-interactive as it gets, but the computers constantly talk back and forth.