What Do They Mean

[Flintstone61]

viewing footage while also recording will obviously cause an increase in throughput to the CPU. You can't escape that. it is now multiasking at a higher level.
My i5-4590 goes from 22% to 26% if I replay a recorded video from 1 camera with 24/7 continous record on all cameras. I'm sure some cpu's might not bat an eye at playback if they arent too busy.

 

[Lawnboy1]

Yes, you are not running the substreams. That will drop you CPU% down to low/mid single digits.

And what cameras are those? FPS and iframes should match. KEY is a ratio of the iframes. BI likes the KEY to be 1.00 and will go into warning status (little yellow triangle) when it drops below 0.4.

Look at the optimization wiki and do EVERY item. Ask if you don't understand something.

Optimizing Blue Iris's CPU Usage

Blue Iris uses a lot of CPU time. In most Blue Iris installations, your CPU is the limiting factor which determines how many cameras you can have. As such, it is extremely important to optimize your configuration to ensure you can get the most out of your system while consuming the least...

ipcamtalk.com

Damn!!! That's what that's for! I'll go back and check my work Professor!