Had my Pioneer AVH-P4100DVD for 2 days now and had a similar problem with playing video from my iPhone 3GS. I originally linked mine up using the generic ipod USB lead and a standard 3.5MM audio jack from the back of the unit to my iPhone. With this setup i could only manage to hear sound from my iPhone movies with a blank screen. I then bought a genuine Pioneer CD-IU200V lead and now i can get video. Its the smaller jack part on that lead (looks like an audio jack) thats sending the picture to Pioneer headunit. The lead DOES need to be put direct in to the back of the unit and not run with an
