Yes, Jami calls are p2p whenever possible, and TURN is used when not (e.g. due to overly restrictive firewalls).

Yes, Jami supports conferencing. One can add additional participants to a 1-on-1 call on the fly, effectively making it a conference. Alternatively, one can enable rendezvous mode from account settings, in which case incoming calls to that account will be added to a conference (similar to a Jisti room).

Amazing. Are there any optimizations for video conferencing in case one participant doesn't have upload bandwidth to stream his video to 10 different IP addresses at once?

I was fidgeting with the tought of something like a overlay multicast network on top of unicast IP, since RFC 1770 was deprecated/never implemented.

Right. In Jami by default only the host of a conference/rendezvous-point will stream to/from all peers and mix their streams, and other peers normally only stream to/from the conference host. Also Jami can automatically adjust the call's bitrate on the fly depending on the link quality:

https://docs.jami.net/user/faq.html#how-much-bandwidth-do-i-...

Hope this helps. :)

Nice! Thank you for the link!