An interior rearview mirror system and assembly includes a variable reflectivity reflective element and a video display screen disposed behind the reflective element and operable to display images viewable through the reflective element by a person viewing the interior rearview mirror assembly when it is normally mounted in a vehicle. The video display screen may be operable to brighten or enhance the intensity of images displayed by the video display screen responsive to a dimming condition of the variable reflectivity reflective element. The mirror system may include an image sensor and a decoder that decodes an output signal of the image sensor. The decoder has a microprocessor operable to control the video display screen, such that the captured image data are processed and images are displayed via operation of a common microprocessor. A compass chip may connect to a vehicle wire harness that extends from a vehicle headliner.