[iPhone developer:tips]; » Audio

Playing Sounds/Audio – AVAudioPlayer

John Muchow — Mon, 07 Dec 2009 10:05:57 +0000

I previously wrote about using Audio Session Services which offers a quick and easy approach for playing short sounds. However, there are a number of limitations, including no control over the volume, playing time is limited to 30 seconds and the only file types supported are AIFF, WAV and CAF.

Sounds with AVAudioPlayer

AVAudioPlayer offers a much wider range of capabilites, including pausing playback, adjusting the volume, tinkering with the playback time (setting and detecting) as well as features for monitoring audio peaks and averages.

The code below shows the basics for setting up a player and playing a sound:

 
AVAudioPlayer  *player;
NSString       *path;
NSError        *error;
 
// Path the audio file
path = [[NSBundle mainBundle] pathForResource:@"sound-file" ofType:@"mp3"];
 
// If we can access the file...
if ([[NSFileManager defaultManager] fileExistsAtPath:path]) 
{    
  // Setup the player
  player = [[AVAudioPlayer alloc] initWithContentsOfURL:
     [NSURL fileURLWithPath:path] error:&error];
 
  // Set the volume (range is 0 to 1)
  player.volume = 0.4f;
 
  // To minimize lag time before start of output, preload buffers      
  [player prepareToPlay];
 
  // Play the sound once (set negative to loop)
  [player setNumberOfLoops:0];
 
  [player play];    
 
}    
 
...
 
// Cleanup
if (player != nil)
{
  if (player.isPlaying == YES)
    [player stop];
  [player release];
}

Silent Mode Switch and Playing Sounds

John Muchow — Wed, 01 Jul 2009 02:50:53 +0000

In a previous tip, Playing Short Sounds, I wrote an example to show how you can play a short sound, up to 30 seconds, by calling one of the C-based functions in the Audio Session Services library.

There is one aspect of this that can be troublesome – by default, playing an Audio Session sound will ~not~ respect the setting of the mute switch on the iPhone. In other words, if you make a call to play a sound and the silent (hardware) switch on the iPhone is set to silent, you’ll still hear the sound.

To respect the setting of the silent switch, add this code above any calls to play a sound:

// Choose a category identifier for audio sessions
UInt32 sessionCategory = kAudioSessionCategory_SoloAmbientSound;
 
// Set the session property
AudioSessionSetProperty(kAudioSessionProperty_AudioCategory,
    sizeof(sessionCategory), &sessionCategory);

There are a number of pre-defined session categories, many will have the same end result as the kAudioSessionCategory_SoloAmbientSound that I opted to use.

Playing Sounds/Audio – Audio Session Services

John Muchow — Sat, 27 Jun 2009 05:09:33 +0000

If you need to play short sounds, less than 30 seconds, Audio Session Services are your friend. Here is a snippet of code to play a wav file:

SystemSoundID soundID;
NSString *path = [[NSBundle mainBundle]
   pathForResource:@"RapidFire" ofType:@"wav"];    
 
AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:path],&soundID);
AudioServicesPlaySystemSound (soundID);

For this to work, you will need to import header file, and also add the AudioToolbox.framework to your project.

For those interested in a little background information, Audio Session Services is a set of functions written in C. There are a few subtleties that give this away. Here is the definition for the AudioServicesCreateSystemSoundID function:

OSStatus AudioServicesCreateSystemSoundID (
   CFURLRef       inFileURL, 
   SystemSoundID  *outSystemSoundID);
);

The giveaway is how we call this function:

AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:path],&soundID);

Notice the parameter outSystemSoundID, which is a pointer to SystemSoundID, a 32 bit unsigned integer. To pass this value as a pointer in C, you pass the address of the variable, which is done using &soundID.

More tips on Audio Session Services in the works…