AVAudioPlayer fade volume out

Question

I have an AVAudioPlayer playing some audio (duh!)

The audio is initiated when the user presses a button. When they release it I want the audio to fade out.

I

Answer 1

I tackled this problem using an NSOperation subclass so fading the volume doesn't block the main thread. It also allows fades to be queued and and forgotten about. This is especially useful for playing one shot sounds with fade-in and fade-out effects as they are dealloced after the last fade is completed.

// Example of MXAudioPlayerFadeOperation in NSOperationQueue 
 NSOperationQueue *audioFaderQueue = [[NSOperationQueue alloc] init];
  [audioFaderQueue setMaxConcurrentOperationCount:1]; // Execute fades serially.

  NSString *filePath = [[NSBundle mainBundle] pathForResource:@"bg" ofType:@"mp3"]; // path to bg.mp3
  AVAudioPlayer *player = [[[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:filePath] error:NULL] autorelease];
  [player setNumberOfLoops:-1];
  [player setVolume:0.0];

  // Note that delay is delay after last fade due to the Operation Queue working serially.
  MXAudioPlayerFadeOperation *fadeIn = [[MXAudioPlayerFadeOperation alloc] initFadeWithAudioPlayer:player toVolume:1.0 overDuration:3.0];
  [fadeIn setDelay:2.0];
  MXAudioPlayerFadeOperation *fadeDown = [[MXAudioPlayerFadeOperation alloc] initFadeWithAudioPlayer:player toVolume:0.1 overDuration:3.0];
  [fadeDown setDelay:0.0];
  MXAudioPlayerFadeOperation *fadeUp = [[MXAudioPlayerFadeOperation alloc] initFadeWithAudioPlayer:player toVolume:1.0 overDuration:4.0];
  [fadeUp setDelay:0.0];
  MXAudioPlayerFadeOperation *fadeOut = [[MXAudioPlayerFadeOperation alloc] initFadeWithAudioPlayer:player toVolume:0.0 overDuration:3.0];
  [fadeOut setDelay:2.0];

  [audioFaderQueue addOperation:fadeIn]; // 2.0s - 5.0s
  [audioFaderQueue addOperation:fadeDown]; // 5.0s - 8.0s
  [audioFaderQueue addOperation:fadeUp]; // 8.0s - 12.0s
  [audioFaderQueue addOperation:fadeOut]; // 14.0s - 17.0s

  [fadeIn release];
  [fadeDown release];
  [fadeUp release];
  [fadeOut release];

For MXAudioPlayerFadeOperation class code see this post.