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How can I play a background audio while my application is running?

Thanks.

Kriem
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ebaccount
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2 Answers2

9

Okay. This is a solution for background sound on iOS4 & iOS5 (definitely works up to iOS 5.0.1), and I have tested it only with AVPlayer. It should probably work for MPMusicPlayerController too.

Required frameworks:

  • AVFoundation.framework
  • AudioToolbox.framework

In your Info.plist, for the key UIBackgroundModes, add audio.

In MyAppDelegate.h:

  • reference <AVFoundation/AVFoundation.h> & <AudioToolbox/AudioToolbox.h>

  • implement the protocol AVAudioSessionDelegate:

    @interface MyAppDelegate : NSObject <UIApplicationDelegate, AVAudioSessionDelegate>

  • define a method ensureAudio:

    // Ensures the audio routes are setup correctly
- (BOOL) ensureAudio;

In MyAppDelegate.m:

  • implement the ensureAudio method:

    - (BOOL) ensureAudio
{
    // Registers this class as the delegate of the audio session (to get background sound)
    [[AVAudioSession sharedInstance] setDelegate: self];  

    // Set category
    NSError *categoryError = nil;
    if (![[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:&categoryError]) {
        NSLog(@"Audio session category could not be set"); 
        return NO;
    }

    // Activate session
    NSError *activationError = nil;
    if (![[AVAudioSession sharedInstance] setActive: YES error: &activationError]) {
        NSLog(@"Audio session could not be activated");
        return NO;
    }

    // Allow the audio to mix with other apps (necessary for background sound)
    UInt32 doChangeDefaultRoute = 1;
    AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryMixWithOthers, sizeof(doChangeDefaultRoute), &doChangeDefaultRoute);

    return YES;
}

  • in the application:didFinishLaunchingWithOptions: method, before you assign the root view controller, run [self ensureAudio]:

    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Configure audio session
    [self ensureAudio];

    // Add the navigation controller's view to the window and display.
    self.window.rootViewController = self.navigationController;
    [self.window makeKeyAndVisible];

    return YES;
}

  • implement the AVAudioSessionDelegate methods like this:

    #pragma mark - AVAudioSessionDelegate

- (void) beginInterruption
{

}

- (void) endInterruption
{
    // Sometimes the audio session will be reset/stopped by an interruption
    [self ensureAudio];
}

- (void) inputIsAvailableChanged:(BOOL)isInputAvailable
{

}

  • ensure that your app continues to run in the background. You can use the ol' [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler] if you want, but I think there are better ways.

  • play the actual audio (note I'm using ARC, that's why there are no release calls):

    NSURL * file = [[NSBundle mainBundle] URLForResource:@"beep" withExtension:@"aif"];    
AVURLAsset * asset = [[AVURLAsset alloc] initWithURL:file options:nil];
AVPlayerItem * item = [[AVPlayerItem alloc] initWithAsset:asset];
__block AVPlayer * player = [[AVPlayer alloc]initWithPlayerItem:item];
__block id finishObserver = [[NSNotificationCenter defaultCenter] addObserverForName:AVPlayerItemDidPlayToEndTimeNotification 
                                                                      object:player.currentItem 
                                                                       queue:[NSOperationQueue mainQueue] 
                                                                  usingBlock:^(NSNotification *note) {
    [[NSNotificationCenter defaultCenter] removeObserver:finishObserver];

    // Reference the 'player' variable so ARC doesn't release it until it's
    // finished playing.
    player = nil;
}];

// Trigger asynchronous load
[asset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:@"tracks"] completionHandler:^{
    // Start playing the beep (watch out - we're not on the main thread here)!
    [player play];
 }];

  • And it shooooooooooooould work!

diachedelic
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  • If you are using MPMusicPlayerController to actually play the music, be sure to use [MPMusicPlayerController iPodMusicPlayer], and not to use [MPMusicPlayerController applicationMusicPlayer]. Also look here: http://stackoverflow.com/questions/1507541/avaudioplayer-turns-off-ipod-how-to-work-around which will show you what to do if you don't want your app to stop whatever music was playing when the user starts your app – Andy Weinstein Jun 06 '12 at 06:59
  • Test this behavior on a physical device. It doesn't work in the Simulator for me. It does work on a physical device. – Webdevotion Jul 13 '12 at 11:57
0

If you are using your app also for recording - then don't forget to change setCategory to AVAudioSessionCategoryPlayAndRecord. In other case you won't be able to record

[[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryPlayAndRecord error:&setCategoryErr];
Kirill Smirnov
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