I cannot seem to get audio media to play in Mobile Safari on iOS 4.2.1 in any situation other than the handler of a click event performed by the user. Even then, if p
As others have said here and according to Apple documentation, MobileSafari does NOT support the autoplay attribute in the video tag. However, in iOS 6 it DOES work. This appears to be a bug which Apple fixed in iOS 6.0.1 (and presumably in iOS 6.1).
Don't rely on autoplay working in iOS 6 if you happened to stumble across it working in iOS 6.0.
-Michael