Video / audio out of sync on static movies played by MPMoviePlayerController

[gc2010]

I have an iPad 1 with iOS 4.2, running an app compiled using Xcode 3.2.5.
The app is implemented using cocos2D framework 1.0.

At a point somewhere in the middle of the app, I would like to introduce a video cut sequence to my game. I instantiate MPMoviePlayerController and use it to play an embedded mp4 file. Once the video starts playing, however, the audio and video are out of sync by as much as 1 second (which, in this case is a lot).

The video file is encoded using H.264 encoding following the iPad guidelines specified by Apple here. However, I've experimented with a variety of other video and audio formats, but to no avail.

I even tried listening to the MPMoviePlayerLoadStateDidChangeNotification message where the player loadState changes to MPMovieLoadStatePlaythroughOK and waiting for 5 seconds after receiving that message to initiate playback, but that didn't help. Using the autoplay feature of MPMoviePlayerController had no effect either.

Does anyone have any suggestions of what else I could try? I couldn't find the mention of this issue anywhere on the web, except for here, but that "fix" doesn't quite apply to me since I'm embedding a video mid-game.

[gc2010]

It turns out that MPMoviePlayerController has this enigmatic property called useApplicationAudioSession which is set to YES by default. Setting this property to NO "causes the movie player to use a system-supplied audio session with a nonmixable playback category." (wisdom courtesy Apple docs) and, incidentally, fixes the lag problem.

I rely on CocosDenshion (part of Cocos2D) for audio and perhaps the application audio session, as defined and utilized by CocosDenshion is incompatible with the audio session required by the movie player. This is a total speculation though, as I don't fully understand what's going on underneath the hood.

Either way, if you use the system supplied audio session, the video playback is suddenly in sync.