Hijacking main video signal in a CRT for gaming

[grumpygamer]

Hi everyone, this morning I woke up and I thought:
"I wonder if it would be possible to use the TV dedicated pins for normal tv and re-direct them outside"
What kind of input would I be looking for on the ONEChip or JungleChip? Is this even possible?
I am going full nostalgia and thinking about attaching a raspberry-pi to a crt in the kitchen to play old shows!
Thanks!