This upgrade has been done on 2006 Audi A8L with rear seats entertainment. We used current screen installation, and just replaced OEM DVD changer with Xiaomi TV Stick.
What we used?
Xiaomi MI TV Stick
HDMI -> RCA Converter
12V to 5V converter with 2 USB ports (option)
We need to power 2 devices, Xiaomi MI TV Stick and 12Vto5V Converter.. you can use lighter socket in boot, but in some cars (like A8) it’s all the time power even if the car is turned off.. Need to find power source which is on after turning ignition on.. probably can find something in fusebox which is located also in the boot.
What if i got Apple CarPlay from UpgradeMyAudi.net?
Every our Apple CarPlay / Android Auto comes with HDMI input, which means can connect anything you want what using HDMI, in this case installation of Xiaomi MI TV Stick needs only this stick & usb power which can be easily found on the fusebox near module.