Are there apps/utilities which can measure useage/non-useage of WiFi at any given location?
Netstumbler or whatever other wifi tool is in fdroid repo.
that a 4K video can be compressed to 'about' 3 gigabytes/hour of data
People can compress any video source down to whatever, but they can no longer call it the first thing anymore, only what they compressed it down do. Lossless video compression exists, but isn't generally worth it. Youtube is a waste at 4k for stupid vlogs. But if you want to read a book at 100m, you need glass, aperture, resolution, stability. See customer needs.
that doesn't tell us how much CPU time is needed to do that in real-time. I am doing a google search for: '4k video compression real-time' but I haven't read more than a few results yet.
In software, the defacto opensource tool is ffmpeg.org. People can download a 4K test stream and chart different CPU's ability to handle different levels in realtime.