I just noticed on the back of my newly purchased refurbed Xbox that it has the Video jack labeled Video input and output jack with two arrows pointing in opposite directions.  What input does the Xbox support?  Is it a passthrough?

I guess no one knows what it's for?

mine only has output, weird

I'm sure it's got a purpose. Conversely, the Nes, SNes, PS1, and Sega Master System all had inputs. When the systems were released, these inputs would serve as the systems ability to expand. To my knowledge, these ports, jacks, etc. were never officially used. Maybe that's how the XBOX's input port went too. I'm pulling this answer out of my ass, though.

It's just weird that it just happens to be the Video jack on the Xbox. I haven't cracked her open yet but I'm guessing it's a version 1.0 xbox. Weird that they'd have this thing in the first revision but not the later.

*manhandles xbox out of closet*

Nope not on mine either....

Maybe it's like the port on the early PS1. When Sony realised it was useless, they removed it to save production costs.