How do you setup iPhone to tv with Sony digital media port adapter?

I have a Sony home theatre and this came with it. It only plugs into the back of the theatre nothing els. It has a video out so I plugged a video cable into the back and into the video in on the system.. Then I plugged a cable into the video out on the system and into the AV import on my flatscreen.. I switched the mode to AV on my tv and I tried to play YouTube videos but the TV was just showing blue only audio plays and the video plays on my iPhone... What am I doing wrong? Can someone help?