I have an extensive library of digital video that I have made from my own DVD and Blu-ray collection, and purchased an iPod 3G specifically for use with these plugs (it's the only bit of Apple tech I own). After the 3rd and 4th gen iPods and iPhones, the connector will plug in and charge but won't transmit video back to the screen.
I make frequent use of it when seated in BF; you can find similar plugs on many other carriers' business and first products these days (SQ, OZ, etc.), so the technology is not limited to UA. I hope that the next generation of IFE goes for simple HDMI inputs or something, but for now these are what we have to work with, and they do the job pretty well.
Based on my experiences, I can share some things I've learned:
- You can only stream video from the native "Videos" app in iOS. In other words, stuff that you buy from the iTunes store or things you can import via iTunes from your personal collection. I have a WD Live network drive that I use as a media server, and videos downloaded within that app will not stream through the IFE. If I use iTunes to directly load the same video on to my iPod, it works fine.
- Videos have to be in an iPod format. MPEG4s are okay, but they have to be .m4v, not .mp4. The slightly different codec makes a difference.
- FA announcements will override the audio, but not pause the video. This you must do manually to avoid missing whatever it is you are watching.
- Sometimes it takes a little work to get the system to recognize that your device is plugged in. Only once have I encountered a plug that absolutely refused to work; I frequently have to wiggle the connectors at either end to get the system to notice my device. The iPod or iPhone must be on and unlocked for the system to "discover" it.
Most people don't take advantage of the technology, most likely because their iPhone or iPod wasn't compatible with it by the time it was widely available.