homebridge-camera-ffmpeg + Zoneminder
Hi, thx for the great plugin. In order to integrate fully with Zoneminder it would be great to have
- MQTT payload parsing. For example another plugin (MQQTthing plugin : https://github.com/arachnetech/homebridge-mqttthing/blob/master/docs/Configuration.md#jsonpath) uses jsonpath and it works perfect using a MQTT topic like zoneminder/1$.state where zoneminder/1 is the monitor number 1. 

- With the parsing available, it would great to be able to include an mqtt payload in the still image source, so one could use something like zoneminder/1$.eventid in the still image direction to get the alarmed image like so : 
"zmserverip:port/index.php?view=image&eid=" + **zoneminder/1$.eventid** + "&fid=objdetect&width=600&token=..."

