Our director of facilities would like to keep all video walls rotating constantly on a display on his desk. I currently put an old (about 2009) iMac on the job but it seems to have some troubles keeping up (although I just realized I should hardwire it rather than have all that going via wifi) and gets blazing hot. I'd like to know either what Cisco Meraki recommends or what others are using successfully for this scenario.
This is a specification on the GPU requirements (GPU is the most important requirement).
For my customers, I have been using Lenovo P330 workstations (i7 CPU, 16GB of RAM).
It has (or at least the ones I have been using) have a NVIDIA® Quadro® P1000 card in it. These have 4 x mini Display Port ports on it, so you can easily connect up to 4 monitors. I have been using them with two monitors. One is a big screen with a video wall with 16 cameras. The other monitor is used by the person to review footage, check emails, etc.
A tip - you want to use the latest video drivers from Nividia. The ones supplied by Lenovo are not new enough and won't operate reliably over a period of several days.
Wow 2009 iMac is old. A Mac mini plugged into a TV might be a better option for you.
I don't know anything about a Mac Mini - but I can assure you that an Intel i7 is not able to decode 16 x HD streams and displaying them on a video wall.
If it doesn't have a GPU - you are going to need one.