[old_tv_nut]

By that time, switchers contained circuits that caused the switch to occur during vertical blanking. Also, all the signals from the cameras had the delays adjusted so they were equal at the input of the switcher. Therefore, there was no jumping of the picture when a cut was made from one camera to another.

The matched timing between cameras was also needed to allow special effects like split screen and wipes, because frame synchronizers had not been invented yet.

I believe at that time the switcher worked on R,G,B signals, like three monochrome switchers in parallel. That way, only one chroma signal encoder was used, so there was no worry about color phase changing from camera to camera.