DVD-Players which output an FBAS (PAL) signal can be connected directly to PIN 1 and 7 of the headunits connector B.
So if you are adventures and you like the low (read:VGA) resolution, you can watch videos from an external player that way.
You will also have to bridge GND and reverse CANbus (don't know which PIN,but it is on connector C) to enable the input.
You will loose the rear-view camera that way.
As an alterntive you can buy an LVDS-Switch to be connected directly to the display unit which offers more functionality and inputs.
It will retain the rear-view camera and is a much better solution.
Note: all this will also invalid your cars' registration and warranty and insurance. It also is punishable by law if you get into a accident. Videoplayers visible form the drivers seat are forbidden