Background audio playback does not work

I've searched everything, but can't get this to work consistently. I want to play audio when a remote push notification arrives, when the app is in the background or on the locked screen and the call is muted.

The steps I followed:

1) Set the required background modes to "Application plays audio" in info.plist.

2) In the application: didFinishLaunchingWithOptions: a) set the audio connection category to Play b) activate the audio session. c) make the application receive remote control events and become the first responder

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

  // https://developer.apple.com/library/ios/qa/qa1668/_index.html
  // For playback to continue when the screen locks, or when the Ring/Silent switch is set to silent, use the AVAudioSessionCategoryPlayback
  BOOL result = [audioSession setCategory:AVAudioSessionCategoryPlayback error:&sessionError]; // TODO AVAudioSessionCategorySoloAmbient

  if (!result && sessionError) {
    NSLog(@"AppDelegate error setting session category. error %@", sessionError);
  }
  else {
    NSLog(@"AppDelegate setting session category is successful");
  }

  result = [audioSession setActive:YES error:&sessionError];

  if (!result && sessionError) {
    NSLog(@"AppDelegate error activating audio session. error %@", sessionError);
  }
  else {
    NSLog(@"AppDelegate setting session active is successful");
  }

  [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];
  [self becomeFirstResponder];
}

      

        
        
        
      

    

3) In applicationDidEnterBackground: a) start background job b) receive remote events

- (void)applicationDidEnterBackground:(UIApplication *)application {
  NSLog(@"AppDelegate applicationDidEnterBackground: called");

  NSLog(@"AppDelegate applicationDidEnterBackground: is calling beginBackgroundTaskWithExpirationHandler:");
  [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:NULL];

  NSLog(@"AppDelegate applicationDidEnterBackground: is calling beginReceivingRemoteControlEvents");
  [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];
}

      

        
        
        
      

    

4) When the remote notification arrives, play the audio file

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler {

  _currentItem = [AVPlayerItem playerItemWithURL:[[NSBundle mainBundle] URLForResource:@"Audio" withExtension:@"wav"]];
  _audioPlayer = [AVPlayer playerWithPlayerItem:_currentItem];

  [_currentItem addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew context:nil];
  [_audioPlayer addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew context:nil];

  NSLog(@"playAudio: calling [_audioPlayer play] on audioPlayer %@", _audioPlayer);
  [_audioPlayer play];
}

      

        
        
        
      

    

It works sometimes, but not always. Any ideas how to make this work consistently?