Best dashcam app for android head unit?

[christine_s]

I just---finally, after 2 years of wanting one--- installed my new HU this weekend. It has a DVR line in, so while I was wiring everything I put in a camera to that input. The video feed shows up whenever i tap on the "dvr" icon in apps (which does nothing except display that input). Now, I would like to make that camera be my dashcam. I want something that will just start recording when I start up the car, loop over old video, and never need me to do anything (unless, of course should I need the footage for something). I want it to run in the background and never bother me. Recording to an SD card would be a nice feature.

All the apps I see seem like they're made for turning an old phone into a dashcam. Is there something out there which works best on a HU?

Thanks for your help!