Audio files + xml = audio playback joy. iOS only!
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A set of classes for assembling audio files into sophisticated AVFoundation sequences.

Say you have some audio files in your project that you'd like to play in sequence. Simply feed an XML description of the sequence to AudioSequenceBuilder and it'll return a fully built AVPlayer, ready to play with AVFoundation!

Here's an example from the demo project. It loads the built-in audio files (car-start.m4a, car-vroom.m4a, and car-crash.m4a):

<seq >
	<sound file="car-start" />
	<sound file="car-vroom" />
	<sound file="car-crash" />

And in your Objective-C code:

@property (nonatomic, strong) AVPLayer *player;


	// load the builder
	AudioSequenceBuilder *builder = [[[AudioSequenceBuilder alloc] init ] autorelease];
	// load the document
	NSURL *docUrl = [[NSBundle mainBundle] URLForResource:@"Sample" withExtension:@"xml"];
	[builder loadDocument:docUrl];	

	// build it
	AVPlayer *player = [builder buildPlayer];
	self.player = player;

	// once it's ready, begin playback
	[self.player addObserver:self forKeyPath:@"status" options:0 context:0];

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

	if(object == self.player)
		AVPlayerStatus playerStatus = self.player.status;
		if(playerStatus == AVPlayerStatusReadyToPlay)

			//  play it!
			[self.player play];

In addition to serial playback, sounds can play in the background with the <par> container. Here's the example above with an added background music track:

	<!-- the main sound sequence -->
	<seq >
		<sound file="car-start" />
		<sound file="car-vroom" />
		<sound file="car-crash" />

	<!-- the background sound -->
	<sound file="tension" />

Add To Your Project

The easiest way is to simply drag these core files into your XCode project:


You'll also need to add:

  • the KissXML project
    • I use the KissXML parser because you can modify the XML after you load it, which is very handy
    • You can use another parser, but you'll have to adjust the classnames in a few places.
  • Apple's AVFoundation & CoreMedia frameworks



speed Allows you to set a custom playback speed. The default is 1.0 Example: <sound file="car-start" speed=".25" />

markIn Allows you to set a custom markIn in the source clip, specified in seconds. The default is 0.

markOut Allows you to set a custom markOut in the source clip, specified in seconds. The default is the duration of the clip. For example: <sound file="car-start" markIn=".25" markOut="3.0" />

Experimental Features

Fixed duration

Specifies that a segment should last a given overall duration, fitting the sounds within appropriately.

Here's a 1 min, 25 sec clip. Note that the car-crash sound will be delayed to play at the end:

<seq duration="1:25.0000" >
	<sound file="car-start" />
	<sound file="car-vroom" />
	<padding ratio="1.0" />
	<sound file="car-crash" />

Note: 'duration' is treated as a minimum duration. If the segment extends past the duration it isn't truncated. This behavior may change in future versions.

Note: multiple <padding> sections work as you'd expect; you can have many of them and they add up then divide their ratio padding evenly.


For background tracks that need to repeat to fit their parent:

<par duration="1:25.0000" >
	<seq >
		<sound file="car-start" />
		<sound file="car-vroom" />
		<sound file="car-crash" />

	<sound file="tension" loopToFitParent="loopSimple" />

The background 'tension' track will repeat as many times as needed the parent par.

FF & Rew support

All <sound>s are treated as navigable chapter markers. That is, you can ff & rew to their beginnings. If you include a sound that shouldn't be treated as navigable, such as background sounds, just mark them as navigable='false'.

Like so:

<sound file="tension" navigable="false" />