How does one wire an OSD-enabled external DVR into Fat Shark goggles?

Question

I've recently bought an Eachine Pro DVR which I want to add to my trusty FatShark Attitude v2 goggles.

Wiring the DVR to be able to record video is easy: just solder the DVR's video input wire to the receiver module's output. However this DVR also has a video output, to which it can display its own OSD and menus, or replay recorded footage.

I'd like to take advantage of these features, which means I need to wire that output back into the goggles somehow.

As far as I know, Fatshark's own builtin DVR in their later models also has an in-goggle OSD and video replay, and apparently it's wired right into the module's video feed such that its output gets intermixed with the original signal and the menus look transparent unless you turn off the module. Does that mean it's okay for me to wire the DVR's output directly to the module's output (essentially shorting it with its own input pin)?

Or do I have to somehow splice the DVR into the signal path, so that the goggles will see only the DVR's output at their input? Is such a splice going to degrade the latency of my goggles if I do? If I do the splicing, what's the best way of going about it? I'm good enough at soldering to cut traces and solder tiny wires to them, but I'd rather not do that if I can avoid it.

Answer 1

I have an external fpv monitor with this DVR and if I watch the DVR live feed a delay in the video image is noticable. If the DVR does lock up while flying you are in big trouble. So I'd strongly advise against the "fly via DVR output" solution.

But there is another solution: You can connect the DVR output to the usual AV input of the goggles (next to the power plug). On the bottom side of the googles there is a switch to turn off the receiver module. When the internal module is deactivated the goggles show the video from the AV plug.

This picture shows the pinout of the AV cable (comes with the googles). I don't know if the DVR can be connected to the AV plug permanently or if this would cause interference if the module is active.