In order to use MP4 automator, first install Sonarr and/or Radarr. Before activating the script, make any desired changes in /opt/appdata/sonarr|radarr/mp4_automator/autoProcess.ini. More info on the options here, please note that the API key section is not necessary in our case, only make the needed processing settings edits.
In order to activate the script, go to Settings >> Connect and create a new "Custom Script". Name it "postSonarr|Radarr.py" and point it at "/sickbeard_mp4_automator/postSonarr|Radarr.py". Enable "On Download" and "On Upgrade" and disable "On Grab" and "On Rename", as shown in the attached picture.
It is highly recommended you edit your move script (/opt/appdata/plexguide/move|-en.sh, depending on if you are encrypted or not) and add
--exclude="**.mkv" in order to prevent unaltered and unfinished files from being uploaded to GD by it.