We usually use a standard USB serial interface and a miniature relay.
It depends a bit on the way your video mixer outputs the tally signals for the control. Usually it is an open-collector circuit. Some devices actually short-circuit two pins of the connection socket.
From a purely technical point of view, PLAYDECK outputs a data stream via TX when GPIO remote control is activated. When this runs back into the system via RX, PLAYDECK starts playback.
So you have to switch a bridge between TX and RX with your interface.
The image shows a “USB TTL adapter” connected to a minituare relay connected to a COM port.
Setting in PLAYDECK
After inserting the USB TTL adapter into the PC, a new COM port will become available to activate in PLAYDECK.