OEM backup camera resolution?
 

As title says, do you know if it's 720p or something else?
Thanks!

On my Pioneer headunit with 800x480 resolution the backup image has been stretched to fill. So my guess would be less than that.

Head unit or mirror?
Pretty sure that the postage stamped size one in the mirror is very high resolution. You just need better than 20/20 vision to see anything in it. It is a total write off if you have bifocals.

car audio is still firmly entrenched in analog technology. that means it's a bog standard 480i composite video signal.

480i. Got it, thanks!