Using kAudioSessionProperty_OtherMixableAudioShouldDuck on iPhone

Question

Hello,

I'm trying to get consistant behavior out of the kAudioSessionProperty_OtherMixableAudioShouldDuck property on the iPhone to allow iPod music blending and I'm having trouble. At the start of my app I set an Ambient category like so:

-(void) initialize
{
 [[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryAmbient error: nil];
}

Later on when I attempt to play audio I set the duck property using the following method:

//this will crossfade the audio with the ipod music
- (void) toggleCrossfadeOn:(UInt32)onOff
{
 //crossfade the ipod music
 AudioSessionSetProperty(kAudioSessionProperty_OtherMixableAudioShouldDuck,sizeof(onOff),&onOff);
 AudioSessionSetActive(onOff);
}

I call this passing a numeric "1" just before playing audio like so:

  [self toggleCrossfadeOn:1];
  [player play];

I then call the crossfade method again passing a zero when my app's audio completes using a playback is stopping callback like so:

-(void) playbackIsStoppingForPlayer:(MQAudioPlayer*)audioPlayer
{
  NSLog(@"Releasing player");
  [audioPlayer release];
  [self toggleCrossfadeOn:0];
}

In my production app this exact code works as expected, causing the ipod to fade out just before playing my app's audio then fade back in when the audio finishes playing. In a new project I recently started, I get different behavior. The iPod audio fades down and never fades back in. In my production app I use the AVAudioPlayer where in my new app I've written a custom audio player that uses audio queues. Could somebody help me understand the differences and how to properly use this API?

Answer 1

I just found part of the problem. It appears to be timing related. I believe my custom player is still feeding the audio system when I make the call to blend the audio back in. If I set a break point in the playbackIsStoppingForPlayer method then it appears to work as expected as the breakpoint stops execution long enough for the remaining audio to finish making its way through the audio queues.