Detecting Active Avaudiosessions on iOS Device

Detecting active AVAudioSessions on iOS device

The way you manage your application's Audio Session has had some significant changes since iOS 6.0, and deserves a brief mention first. Before iOS 6.0 you would make use of AVAudioSession and AudioSessionServices classes, incorporating delegation and property listening respectively. From iOS 6.0 onwards use AVAudioSession class and incorporate notifications.

The following is for iOS 6.0 onwards.

To tell if other audio outside your applications sandbox is playing use -

// query if other audio is playing
BOOL isPlayingWithOthers = [[AVAudioSession sharedInstance] isOtherAudioPlaying];
// test it with...
(isPlayingWithOthers) ? NSLog(@"other audio is playing") : NSLog(@"no other audio is playing");

As for interruption handling you'll need to observe AVAudioSessionInterruptionNotification and AVAudioSessionRouteChangeNotification. So in the class that manages your audio session you could put something like the following - this should be called once at the start of the application lifecycle and don't forget to remove observer in the dealloc method of the same class.

// ensure we already have a singleton object
    [AVAudioSession sharedInstance];
    // register for notifications
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(interruption:)
                                                 name:AVAudioSessionInterruptionNotification
                                               object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(routeChange:)
                                                 name:AVAudioSessionRouteChangeNotification
                                               object:nil];

And finally add the following selectors interruption: and routeChange: - these will receive a NSNotification object that has a property called userInfo of type NSDictionary that you read to assist any conditionals your application has.

- (void)interruption:(NSNotification*)notification {
// get the user info dictionary
NSDictionary *interuptionDict = notification.userInfo;
// get the AVAudioSessionInterruptionTypeKey enum from the dictionary
NSInteger interuptionType = [[interuptionDict valueForKey:AVAudioSessionInterruptionTypeKey] integerValue];
// decide what to do based on interruption type here...
switch (interuptionType) {
    case AVAudioSessionInterruptionTypeBegan:
        NSLog(@"Audio Session Interruption case started.");
        // fork to handling method here...
        // EG:[self handleInterruptionStarted];
        break;

    case AVAudioSessionInterruptionTypeEnded:
        NSLog(@"Audio Session Interruption case ended.");
        // fork to handling method here...
        // EG:[self handleInterruptionEnded];
        break;

    default:
        NSLog(@"Audio Session Interruption Notification case default.");
        break;
} }

And similarly...

- (void)routeChange:(NSNotification*)notification {

NSDictionary *interuptionDict = notification.userInfo;

NSInteger routeChangeReason = [[interuptionDict valueForKey:AVAudioSessionRouteChangeReasonKey] integerValue];

switch (routeChangeReason) {
    case AVAudioSessionRouteChangeReasonUnknown:
        NSLog(@"routeChangeReason : AVAudioSessionRouteChangeReasonUnknown");
        break;

    case AVAudioSessionRouteChangeReasonNewDeviceAvailable:
        // a headset was added or removed
        NSLog(@"routeChangeReason : AVAudioSessionRouteChangeReasonNewDeviceAvailable");
        break;

    case AVAudioSessionRouteChangeReasonOldDeviceUnavailable:
        // a headset was added or removed
        NSLog(@"routeChangeReason : AVAudioSessionRouteChangeReasonOldDeviceUnavailable");
        break;

    case AVAudioSessionRouteChangeReasonCategoryChange:
        // called at start - also when other audio wants to play
        NSLog(@"routeChangeReason : AVAudioSessionRouteChangeReasonCategoryChange");//AVAudioSessionRouteChangeReasonCategoryChange
        break;

    case AVAudioSessionRouteChangeReasonOverride:
        NSLog(@"routeChangeReason : AVAudioSessionRouteChangeReasonOverride");
        break;

    case AVAudioSessionRouteChangeReasonWakeFromSleep:
        NSLog(@"routeChangeReason : AVAudioSessionRouteChangeReasonWakeFromSleep");
        break;

    case AVAudioSessionRouteChangeReasonNoSuitableRouteForCategory:
        NSLog(@"routeChangeReason : AVAudioSessionRouteChangeReasonNoSuitableRouteForCategory");
        break;

    default:
        break;
} }

There is no need to poll anything as long as you check the state of your applications audio session say for example in the viewDidLoad of your root view controller, at the start of you apps lifecycle. Any changes from there onwards to your applications audio session will be known via these two main notifications. Replace the NSLog statements with what ever your code needs to do based on the cases contained in the switch.

You can find more information about AVAudioSessionInterruptionTypeKey and AVAudioSessionRouteChangeReasonKey in the AVAudioSession class reference documentation.

My apologies for the long answer but I think Audio Session management in iOS is rather fiddly and Apple's Audio Session Programming Guide, at the time of writing this, does not include code examples using notifications for interruption handling.

AVAudioSession category not working as documentation dictates

I think I managed to work it out - turns out that it has nothing to do with my app at all, but rather the iPod app. My app obeys the mute switch as it should when the iPod isn't playing, and then allows the iPod to play over it - all behaviour I wanted. However, when the iPod is playing, the app stops responding to the mute switch, so I think it's just something the iPod does to the device audio settings. I could probably work a way around it if I really wanted to spend the time on it, but as long as it obeys the mute switch when the iPod isn't playing that's good enough for me.

EDIT: to work around this, just use this function to determine whether or not the mute switch is on manually, and don't play your sounds if the result is YES. Could be a bit of a pain if you don't have a central audio manager class, though. It would be nice if Apple could publish this behaviour in their documentation.

- (BOOL)deviceIsSilenced
{
    #if TARGET_IPHONE_SIMULATOR
    // return NO in simulator. Code causes crashes for some reason.
    return NO;
    #endif

    CFStringRef state;
    UInt32 propertySize = sizeof(CFStringRef);
    AudioSessionInitialize(NULL, NULL, NULL, NULL);
    AudioSessionGetProperty(kAudioSessionProperty_AudioRoute, &propertySize, &state);

    return (CFStringGetLength(state) <= 0);
}

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