Video splitter hardware design and devices?

[Roger Lin]

I have a standalone control unit receiving four video inputs and its
output is connected to a TV monitor. I am thinking to put a video
splitter into my control unit and I can monitor my four videos at the
same time. Any good color video splitter device/module on the
market? How much? If I need to design the circuits, any good example
I can start with?

TIA

Roger