intercom talkback or doorphone video/ audio

hi every one
i need some information about intercom system Audio and video what modules is needed and how they work,
every kind of information will be useful

I would check for the brand and model number if they are on the back of the units, then google for a manual for it.

hi , i don't care about BRAND , I'm looking for some general information about door phone ( intercom) . i want to know how they use to connect
video(camera) and audio and how they perform it in monochrome and color systems , if they use 3 wire for RGB or they Use Y , C , and so ...
how they connect CRT display and , TFT display