Nextcloud 18 on docker: Talks application explanation

I remember some time ago having major issue with talks app and video/audio feed.
I remember at that time that nextcloud was using by default an open Turn Server hosted by Nextcloud (I might be wrong.)
Any way it was trouble some for many user to have Talks working.
Nowadays I feel like it’s working really nicely, I don’t know if it’s due to browser/Nextcloud updates, but it works flawlessly.
I would like to understand how it works what kind of load I can expect on my server and where the STUN and TURN server are hosted.
Do they run inside the docker ? do they run on a third party server I’m not aware of (and if so how to change that)
Thank you very much for your help.