What would happen if you short two video signals together?

You'll be fine with the switch you have.

Video signals are low voltage and the power is limited by the source impedance. Some video switches even deliberately short out all deselected inputs to avoid ghosting from the unneeded signals.

Don

there is no problem because of shorting. however when viewing, you will get a picture "roll" because the 2 sources are not synchronized. so the picture glitch might be annoying if you switch a lot. also if you are trying to record the feed, the recorder might stop or at the very least glitch because of the disruption in synch.

we are assuming you mean analog type video, and not digital. with digital you will also get a picture disruption, but i am not sure how annoying it would be cause i've never done that.

What will happen? Not much. You're dealing with a 75 ohm source that's designed to drive a 75 ohm load. Connecting them together will mean they are trying to drive each other, which isn't terrible. But frankly if I were you I would go find a break-before-make-switch.

Try it and you know right away. Makes no harm to them.