OR is opensource so you can pretty much explore it on your own but TLDR is that it records diffs of DOM, network and state alongside with mouse and send it as a

OR is opensource so you can pretty much explore it on your own but TLDR is that it records diffs of DOM, network and state alongside with mouse and send it as a byte array batches to the backend that gzip this files, and then this process is going the other way (unpack, bytes to diff to display) in the player parts. Videos would take too much space plus API is limited as I can see on MDN