AVQueuePlayer and audio session issue - iphone

Question

I am going to try to give a detailed account of my issue.
I have an app that is in the store that uses in app sound. Currently I am using AVQueuePlayer because some of the sound will overlap and allow it to play in order. A lot of this sound is being played while I am playing embedded videos using AVPlayer which may not matter at all. The problem is that I am having reports of the sound stopping across the entire app. I am unable to reproduce this myself but we have a lot of active users and it is reported by some. Whenever it is reported and we determine its not just the silent switch or the sound volume down restarting the app always solves the problem. Occasionally we've heard of the sound magically returning with no changes. I have also had a couple of reports that it happens when using airplay and bluetooth but that may just be an complication of the problem or coincidence.
Below is the code that I am using and maybe I'm just using a setting wrong or not using a setting that I should be but this code works 99.9% of the time.
I use ducking for all sounds I play to lower the volume of the user's iPod music.
Here is my initialization in appDidFinishLaunchingWithOptions (Maybe its not needed at all in the start and sorry for the mixing of conventions):
AudioSessionInitialize (NULL, NULL, NULL, NULL);
[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];
UInt32 sessionCategory = kAudioSessionCategory_AmbientSound;
AudioSessionSetProperty (kAudioSessionProperty_AudioCategory, sizeof (sessionCategory), &sessionCategory);
[[AVAudioSession sharedInstance] setActive:YES withFlags:AVAudioSessionSetActiveFlags_NotifyOthersOnDeactivation error:nil];
When I play a sound:
-(void)playSound: (NSString *)soundString
{
OSStatus propertySetError = 0;
UInt32 allowMixing = true;
propertySetError |= AudioSessionSetProperty(kAudioSessionProperty_OtherMixableAudioShouldDuck, sizeof(allowMixing), &allowMixing);
[[AVAudioSession sharedInstance] setActive:YES withFlags:AVAudioSessionSetActiveFlags_NotifyOthersOnDeactivation error:nil];
NSURL *thisUrl = [NSURL fileURLWithPath:[NSString stringWithFormat:#"%#/%#.caf", [[NSBundle mainBundle] resourcePath], soundString]];
AVPlayerItem *item = [[AVPlayerItem alloc] initWithURL:thisUrl];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(reachedEndOfItem:)
name:AVPlayerItemDidPlayToEndTimeNotification
object:item];
if(_audioPlayerQueue == nil)
{
_audioPlayerQueue = [[AVQueuePlayer alloc] initWithItems:[NSArray arrayWithObject:item]];
}
else
{
if([_audioPlayerQueue canInsertItem:item afterItem:nil])
{
[_audioPlayerQueue insertItem:item afterItem:nil];
}
}
if(_audioPlayerQueue == nil)
{
NSLog(#"error");
}
else
{
[_audioPlayerQueue play];
}
return;
}
When the sound finishes playing:
- (void)reachedEndOfItem: (AVPlayerItem*)item
{
[self performSelector:#selector(turnOffDucking) withObject:nil afterDelay:0.5f];
}
- (void)turnOffDucking
{
NSLog(#"reached end");
[[AVAudioSession sharedInstance] setActive:NO withFlags:AVAudioSessionSetActiveFlags_NotifyOthersOnDeactivation error:nil];
OSStatus propertySetError = 0;
UInt32 allowMixing = false;
propertySetError |= AudioSessionSetProperty(kAudioSessionProperty_OtherMixableAudioShouldDuck, sizeof(allowMixing), &allowMixing);
}
Any insight on what I am doing wrong, what settings I should be using for the audio session or known bugs/problems would be very helpful. I would be willing to look into using a different audio engine as this can have some slight performance issues when playing a video and having iPod music playing in tandem but I'd rather stick with this method of playing audio.
Thank you for any help you can provide.
-Ryan

Answer 1

I had a similar issue in past and found out that concurrent thread access was the reason.
Specifically, I think calling performSelectorAfterDelay could be the reason if another thread tries to modify the audio session at the same time the delay ends, as then we'll have two different threads trying to access the audio session.
So, I suggest to check your code again and make sure all calls to playSound are made from the main thread. Also, it may be better to use performSelectorOnMainThread instead of performSelectorAfterDelay as the docs say:
Invocations of blocks, key-value observers, or notification handlers are not guaranteed to be made on any particular thread or queue. Instead, AV Foundation invokes these handlers on threads or queues on which it performs its internal tasks.