It took me quite some time to figure out how to transmit A.high quality, B.low latency and C.low cost video to the back wall in the speaker room even when there is no internet access. The hardware works like that:
Panasonic/Fuji -> ANNNWZD 1m HDMI cable -> CAM LINK 4K Elgato -> Macbook Pro
The CAM LINK 4K is automatically recognized as a webRTC resource without any further software. As server software I installed easyrtc, a low level webRTC library.
cd /easyrtc/server_example node server_ssl.js
Using the Chrome browser we can now open https://localhost:8443/demos/demo_multistream.html where I adjusted the layout using pure buttons.
The second window (in front) is then send full screen to the projector. Lag is less than .2s which is acceptable.