playing background audio on iphone - iphone

Question

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

Answer 1

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!

Answer 2

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];