Tutorial: Easy Audio Playback With AVAudioPlayer

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The iPhone SDK’s AVFoundation framework includes AVAudioPlayer, an easy, feature rich, Objective-C based way of playing audio files.

This tutorial demonstrates how to use AVAudioPlayer. When you’ve finished the tutorial you’ll have created a simple app that plays an MP3 audio file in a loop when the app starts.

Source/Github

The code for this tutorial is available on GitHub. You can either clone the repository or download this zip.

Creating The Project

Launch Xcode and create a new View-Based iPhone application called AudioPlayer:

  1. Create a new project using File > New Project… from Xcode’s menu
  2. Select View-based Application from the iPhone OS > Application section, click Choose…
  3. Name the project as AudioPlayer and click Save

Adding The AVFoundation Framework

In order to use the SDK’s AVAudioPlayer class, we’ll need to add the AVFoundation framework to the project:

  1. Expand the Targets branch in the Groups & Files panel of the project
  2. Control-click or right-click the AudioPlayer item
  3. Choose Add > Existing Frameworks…
  4. Click the + button at the bottom left beneath Linked Libraries
  5. Choose AVFoundation.framework and click Add
  6. AVFoundation.framework will now be listed under Linked Libraries. Close the window

Next, we’ll import the AVFoundation headers in our view controller’s interface file and set up an AVAudioPlayer instance variable:

  1. Expand the AudioPlayer project branch in the Groups & Files panel of the project
  2. Expand the Classes folder
  3. Edit AudioPlayerViewController.h by selecting it
  4. Update the file. Changes are bold:

#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>

@interface AudioPlayerViewController : UIViewController {
	AVAudioPlayer *audioPlayer;
}

@end

Adding An Audio File

We’ll need an audio file for playback. We’ll, unimaginatively, call the fille audiofile.mp3. Add it to the project:

  1. Control-click or right click on the Resources folder in the Groups & Files panel of the project
  2. Select Add > Existing Files… from the context menu
  3. Locate and select the file for import and click Add
  4. Check the Copy items into destination group’s folder (if needed) box and click Add

Starting Audio Playback

We’ll start the audio playback in ViewDidLoad:

  1. Uncomment the boilerplate ViewDidLoad method
  2. Update it as follows. Changes are bold:

- (void)viewDidLoad {
	[super viewDidLoad];

	NSURL *url = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/audiofile.mp3", [[NSBundle mainBundle] resourcePath]]];
	
	NSError *error;
	audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:&error];
	audioPlayer.numberOfLoops = -1;
	
	if (audioPlayer == nil)
		NSLog([error description]);				
	else 
		[audioPlayer play];

}

AVAudioPlayer is initialized with a URL, so we create one whose path points to the audio file in our on-the-phone resources directory. Setting the audio player’s numberOfLoops property to a negative number causes it to loop indefinitely. After configuring the player, we start the playback by sending the play message to the object.

Remember to release the audioPlayer in dealloc. Changes are bold:

- (void)dealloc {
	[audioPlayer release];
	[super dealloc];
}

More Capabilities

You can adjust the volume of the player, check/set the time played so far and pause or stop playback:

audioPlayer.volume = 0.5; // 0.0 - no volume; 1.0 full volume
NSLog(@"%f seconds played so far", audioPlayer.currentTime);
audioPlayer.currentTime = 10; // jump to the 10 second mark
[audioPlayer pause]; 
[audioPlayer stop]; // Does not reset currentTime; sending play resumes

Finally, you can implement the AVAudioPlayerDelegate protocol to, among other things, be notified when audio finishes playing — perhaps to move onto the next song in a playlist.


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