This might not be my most popular post but I haven’t found anything that demonstrates the possibility of doing this – especially with a dashcam/aftermarket head unit in a car. Hopefully it’s helpful to someone!
The issue I had was that I already wired up a reverse camera (3.5mm) to my Rexing V1P dashcam and my new Sony XAV-AX100 headunit had an (RCA) input for a reverse camera. I didn’t want to have two cameras off the back of my car so I attempted to split the feed.
As you can see in the photo above, the 3.5mm aux cord comes from the camera (to the right) and a female 3.5mm aux to male RCA converts the digital feed to analog. Then, I used an RCA coupler to connect the white RCAs and a female RCA (yellow) to the red. The female RCA wires are then stripped and split so that one can return to the head unit and the other can complete the circuit to the dashcam (another aux to RCA cord).
I have no idea how this works but I was also able to make this work with a headphone splitter. One headphone split side went right back to the camera and the other converted to RCA and one of the two RCAs worked as the video feed. So, this might end up being a trial and error kind of thing for you but just know that it IS possible to split a digital camera feed to RCA!