I finally got this thing working on my 8 IP cams. Previously I was running into cpu capacity issues when upgrading from ubuntu 16.04 / zoneminder 1.30.
The following resolved the capacity issue for me. When defining each camera, under the "storage" tab, I set save_jpegs to disabled and video_writer to h.264_pass_through.
At 5 frames a second, I'm getting system monitor reporting under 20% on each of the 4 processors (i think there is actually 2 hardware processors - i7-5600u). its a dell latitude booted from a usb attached sata drive. 16gb ram.