How to choose the stream quality?

Question

Node.js

Good afternoon, tell me which way to dig.
Sat picking up the article:
https://quantizd.com/building-live-streaming-app-w...
The project was assembled, played around and I wanted to figure it out further and actually the choice fell on changing the quality (like 144, 360, 720).
The problem is that having rummaged around on the Internet, the node media server docks, I did not find anything in which direction to look at all, well, except for the videojs settings and the plugin for choosing the quality.
Actually, how I imagine it: we take our source stream and cut it into several options on the server, and the user already chooses the quality.
In general, maybe someone has an example on the topic or what to read, in which direction to look and at what point in time we are cutting this very stream.
Thanks in advance for any help.
UPD I’m looking in the direction of ffmpeg, though I haven’t found any information yet on how to encode everything in a stream and actually at what stage we do it :(