The "AV in" is to hook up a VCR etc through the car system and it will appear on the front screen by selecting AV on the TV channel selector. "AV out" lets you hook up screens in the rear, it mimics the front TV screen and doesn't have the annoying safety message when the vehicle is moving. The button allows rear passengers to select the TV for the rear screens.

In theory you should be able to input audio via the "AV in" jack but you would need a AV 3.5mm plug adaptor not just an audio 2 channel plug. It would be a bit messy because you would have to hae the TV selected to hear the audio which would prevent you from using computer or nav functions at the same time.

A better option would be to buy the Aux in audio cable that plugs into the rear of the radio head unit (behind the screen) and gives you an audio input without preventing use of the other features at the same time. I have done this to run an MP3 player and it works really well.

Hope this helps.

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