actually, most car audio companies, kenwood,pioneer etc, just expect us to tap into a lead that is triggered when the car is not in motion (i.e. a parking brake ground), no tapping into any car computers :)
you would have to GUARANTEE that i could not watch a movie when the car was moving. interesting logic processes that involve interfacing with the vehicle computer to "dis-allow" the running of certain applications while the vehicle is in motion. that involves many hundreds of vehicle computers to design for.