UIAlertView breaks AVPlayer's audio process - ios

Question

I have a basic iOS app that uses an AVPlayer to play local files with an MTAudioProcessingTap attached. I added a UIAlertView pop-up with a text field to allow custom URLs to be added to the app's playlist, but when the alert is shown using [alert show], the audio system fails. If I show the alert before any track has been played, start playing a track, and then show the alert again it works fine — almost as if there's some CPU-spike penalty for the first show (though I can't see anything on instruments).
Alert:
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Play Remote Track"
message:#"Enter the address."
delegate:self
cancelButtonTitle:#"Cancel"
otherButtonTitles:#"Play", nil];
alert.alertViewStyle = UIAlertViewStylePlainTextInput;
[alert show];
Errors:
Log message: <ClientProcessingTapManager> AudioQueueProcessingTapGetSourceAudio posting message to kill mediaserverd (36078)
MTAudioProcessingTapGetSourceAudio() returns status code 268451843 then on the next packet 268435459.
Update: The issue only happens while debugging, so it turns out it's not a showstopper. I'd still be interested in getting to the bottom of it, though.

Answer 1

Try this:
#import <dispatch/dispatch.h>
dispatch_async(dispatch_get_main_queue(), ^{
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Play Remote Track"
message:#"Enter the address."
delegate:self
cancelButtonTitle:#"Cancel"
otherButtonTitles:#"Play", nil];
alert.alertViewStyle = UIAlertViewStylePlainTextInput;
[alert show];
});
If it doesn't help, then try to look on MTAudioProcessingTap Audio Processor Sample Code. I have tried to put your AlertView call to different places while video was showing, and everything was ok - no bugs. It was iPad Simulator v. 6.1.

Answer 2

Just to put this one to bed, I eventually concluded that it was a performance issue. In all other circumstances I've come across, AudioQueueProcessingTapGetSourceAudio posting message to kill mediaserverd (36078) seems to be called when you're doing "too much" work inside the MTAudioProcessingTap process loop. I think showing the UIAlertView in my case was pushing the device over the edge.
As for what constitutes "too much" work, I have no idea, and there's no mention in any of the documentation in the header file for MTAudioProcessingTap. On several devices I tested my app on, I could increase the work done in the audio loop until overall CPU was at about 20%, then the kill message appeared and the tap stopped calling its processing callback. It must either be an artificially imposed limit, or for some reason my process loop couldn't fulfil its real time guarantee regardless of the amount of CPU used.