Maybe you should have a look at my powercontrol kit. My CID 650 LCD panel has a control signal input for selecting AV2 as input. Problem is to get back to VGA afterwards if it was not active when camera was selected. Major problem when the panel is fitted into the dash without the buttons as I have done.
I want it to be totaly automatic. I solved this by enabling VGA for a few seconds before activating AV2, and holding on to VGA 2s after deactivating AV2. Things that can be done with CPU only.