No audio on iOS app using the RemoteIO AudioUnit when the iPad is restarted

Question

I have a strange issue where an iOS app that I have developed works fine when I build and run it from XCode on the device. However, on restarting the device and running the app, I get no audio at all. If I subsequently kill the app and restart it from the device, I start getting audio again. I initially thought it was an Interruption Handler issue, but am not sure any more. Any help would be appreciated!

Here's my interruption handler just in case.

static void MyInterruptionListener (void *inUserData,
                                UInt32 inInterruptionState) {

printf ("Interrupted! inInterruptionState=%ld\n", inInterruptionState);
pediViewController *pediController = (__bridge pediViewController*)inUserData;
switch (inInterruptionState) {
    case kAudioSessionBeginInterruption:
        CheckError (AudioOutputUnitStop (pediController.effectState.rioUnit),
                    "Couldn't start RIO unit");
    case kAudioSessionEndInterruption:
        // TODO: doesn't work!
        CheckError(AudioSessionSetActive(true),
                   "Couldn't set audio session active");
        CheckError (AudioOutputUnitStart (pediController.effectState.rioUnit),
                    "Couldn't start RIO unit");
        break;
    default:
        break;
};

}

Answer 1

The issue went away on upgrading to iOS 6. I did some intensive debugging by commenting out each and every line of code in the audio callback and testing by restarting the iPad and running the app again 3 times each. Finally it was solved by updating to iOS 6 on the device and running on that. I also got a huge performance boost in doing so!

Answer 2

You should handle the app going in and out of the background using the audio route change callback, not the interruption handler.

This is what worked for me anyway when I had a similar problem to your own (If I understand your problem correctly).

Here is an example

AudioSessionAddPropertyListener (
                                     kAudioSessionProperty_AudioRouteChange,
                                     audioRouteChangeListenerCallback,
                                     (__bridge void*) self
                                     );

void audioRouteChangeListenerCallback (
                                       void                      *inUserData,
                                       AudioSessionPropertyID    inPropertyID,
                                       UInt32                    inPropertyValueSize,
                                       const void                *inPropertyValue
                                       ) {

    // Ensure that this callback was invoked because of an audio route change
    if (inPropertyID != kAudioSessionProperty_AudioRouteChange) return;


    AudioEngine *audioObject = (__bridge AudioEngine *) inUserData;

    // if application sound is not playing, there's nothing to do, so return.
    if (NO == audioObject.isPlaying) {

        NSLog (@"Audio route change while application audio is stopped.");
        return;

    } else {

        CFDictionaryRef routeChangeDictionary = inPropertyValue;

        CFNumberRef routeChangeReasonRef =
        CFDictionaryGetValue (
                              routeChangeDictionary,
                              CFSTR (kAudioSession_AudioRouteChangeKey_Reason)
                              );

        SInt32 routeChangeReason;

        CFNumberGetValue (
                          routeChangeReasonRef,
                          kCFNumberSInt32Type,
                          &routeChangeReason
                          );
             if (routeChangeReason == kAudioSessionRouteChangeReason_OldDeviceUnavailable) {

            NSLog (@"Audio output device was removed; stopping audio playback.");
            NSString *MixerHostAudioObjectPlaybackStateDidChangeNotification = @"MixerHostAudioObjectPlaybackStateDidChangeNotification";
            [[NSNotificationCenter defaultCenter] postNotificationName: MixerHostAudioObjectPlaybackStateDidChangeNotification object: audioObject]; 

        } else {

            NSLog (@"A route change occurred that does not require stopping application audio.");
        }
    }
}