The idea about posting in the correct forum is that people who use that app or device are more likely to be there.
However, when I then try to do this on my iPad 3 (again iPhoto 9.3) the format no longer seems supported.
There is no iPhoto 9.3 for iPad. There is iPhoto for iOS, and entirely different application.
I don't believe that the iPad supports AVCHD, but to be sure, best ask someone who uses an iPad regularly, or iPhoto for iOS regularly.
Guess where you find those...