I have designed video switchers for professional/broadcast applications (up to 64 in, 64 out) so am aware of the requirements.
The first problem is that if you have more than 1 output and wish to connect one input to more than 1 output you need an amplifier. This is simply because video inputs are (should be!) terminated in 75 ohms. If you don't have an amplifier you will connect multiple 75 ohm loads to one source resulting in wrong signal levels quite apart from any impedance mismatch.
The other question is timing of the switch. This has been mentioned here but the explanations aren't entirely correct. In a broadcast environment you try to keep signals synchronous, in other words with their field syncs at the same point in time. Hence you can switch between them freely without causing sync disturbance. The switch is usually done on a specific line in the field interval
https://www.document-center.com/stan...8/history/BASE
In a domestic environment the various signals are not synchronous so you might as well take the switch at any random time. You'll get a disturbance regardless. If you wish to switch between non-sync signals without disturbance you need a frame store synchroniser.