Ya.. If you have Apple TV, it has the advantage of wireless. But for certain application which does not support TV out, you can't get full screen by using Apple TV. But if you use Digital AV Adapter, you can set the display ratio to full screen by using DisplayOut from Cydia.
Following is my setup to use iPad for video playing/streaming..
RushPlayer+ from cydia - The best RMVB/MKV Player for IOS . No lagging for 720p/1080p RMVB/MKV video playing. More user friendly User interface than XBMC and RMVB playing is the best in class, MKV playing same as XBMC as it utilizing the native hardware decoding.. That's why it is better than RushPlayer in Appstore.
QVOD for IOS - Use QVOD to download movie online (not playing) and use RushPlayer+ to play it. It will be realtime streaming if you have fast internet access.
DisplayOut from Cydia - To set the mirroing display ratio to full screen.
Digital AV Cable (HDMI) - To output the video to TV via HDMI.
Added on June 30, 2012, 1:21 pmI'm not sure about the 3rd party RCA adapter. But for my 3rd party HDMI adapter, it works well with IOS 4.3.3, IOS 5.01, IOS 5.1.1. Tested working fine, and the quality and features are the same as the Original Apple Digital AV adatper.. but the price is cheaper..
No wonder... I don't JB my iOS devices... too many problems. Rather leave it stock.