How can I implement a SCART switch connector
It would be CONN, SCART, Female, thru-hole PCB mount SCART 21 pin 
https://en.m.wikipedia.org/wiki/SCART

However the square posts may damage if using a plugin proto plug, so solder short resistor wires as pins using 1/4w and cut to length 3mm to have a round connection.

However, these connectors are not common and mostly IDC ribbon interface.

http://www.mouser.com/ds/2/222/K-SCARTX-024-183658.pdf

To MUX RGB, ground and Composite Video , I assume you already understand the interface pins.