A subclass of AVAudioPlayer that retains itself until playback ends or encounters an error, so you don't have to keep a strong reference to it. Supports pass-through to an exogenous delegate that gets set (which is captured in a zeroing weak reference). It's probably inadvisable to use this, but what the heck!

OneShotAVAudioPlayer.h

#import <AVFoundation/AVFoundation.h>

@interface OneShotAVAudioPlayer : AVAudioPlayer
@end

OneShotAVAudioPlayer.m

#import "OneShotAVAudioPlayer.h"
#import <AVFoundation/AVFoundation.h>
#import <objc/runtime.h>

@interface OneShotAVAudioPlayer () <AVAudioPlayerDelegate>
@property(weak) id<AVAudioPlayerDelegate> p_exogenousDelegate;
@end

@implementation OneShotAVAudioPlayer

static void * const OneShotAVAudioPlayerKey = (void*)&OneShotAVAudioPlayerKey;

- (id)initWithContentsOfURL:(NSURL *)url error:(NSError **)outError
{
    if (self = [super initWithContentsOfURL:url error:outError])
	{
		// Retain our
		objc_setAssociatedObject(self, OneShotAVAudioPlayerKey, self, OBJC_ASSOCIATION_RETAIN);
		[super setDelegate: self];
	}
	return self;
}

- (id)initWithData:(NSData *)data error:(NSError **)outError;
{
	if (self = [super initWithData:data error:outError])
	{
		objc_setAssociatedObject(self, OneShotAVAudioPlayerKey, self, OBJC_ASSOCIATION_RETAIN);
		[super setDelegate: self];
	}
	return self;
}

- (void)setDelegate:(id<AVAudioPlayerDelegate>)delegate
{
	self.p_exogenousDelegate = delegate;
}

- (id<AVAudioPlayerDelegate>)delegate
{
	return self.p_exogenousDelegate;
}

- (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag
{
	@try
	{
		if ([self.p_exogenousDelegate respondsToSelector: _cmd])
			[self.p_exogenousDelegate audioPlayerDidFinishPlaying:player successfully:flag];
	}
	@finally
	{
		// Make a strong ref so we stay alive through the scope of this function
		typeof(self) keepAlive = self;
		// Give up the self retain
		objc_setAssociatedObject(keepAlive, OneShotAVAudioPlayerKey, nil, OBJC_ASSOCIATION_RETAIN);
		// Push in the "real" (outside) delegate, cause our job is done here.
		[super setDelegate: self.p_exogenousDelegate];
	}
}

- (void)audioPlayerDecodeErrorDidOccur:(AVAudioPlayer *)player error:(NSError *)error
{
	@try
	{
		if ([self.p_exogenousDelegate respondsToSelector: _cmd])
			[self.p_exogenousDelegate audioPlayerDecodeErrorDidOccur:player error:error];
	}
	@finally
	{
		// Make a strong ref so we stay alive through the scope of this function
		typeof(self) keepAlive = self;
		// Give up the self retain
		objc_setAssociatedObject(keepAlive, OneShotAVAudioPlayerKey, nil, OBJC_ASSOCIATION_RETAIN);
		// Push in the "real" (outside) delegate, cause our job is done here.
		[super setDelegate: self.p_exogenousDelegate];
	}
}

- (BOOL)respondsToSelector:(SEL)aSelector
{
	BOOL retVal = [super respondsToSelector: aSelector];
	if (!retVal)
	{
		struct objc_method_description method = protocol_getMethodDescription(@protocol(AVAudioPlayerDelegate), aSelector, YES, YES);
		if (method.name)
		{
			retVal = [self.p_exogenousDelegate respondsToSelector: aSelector];
		}
	}
	return retVal;
}

- (id)forwardingTargetForSelector:(SEL)aSelector
{
	id retVal = [super forwardingTargetForSelector:aSelector];
	if (!retVal)
	{
		struct objc_method_description method = protocol_getMethodDescription(@protocol(AVAudioPlayerDelegate), aSelector, YES, YES);
		if (method.name && [self.p_exogenousDelegate respondsToSelector: aSelector])
		{
			retVal = self.p_exogenousDelegate;
		}
	}
	return retVal;
}

- (void)setNumberOfLoops:(NSInteger)numberOfLoops
{
    if (numberOfLoops < 0)
    {
        NSLog(@"Warning! You have set an infinite loop count for an instance of OneShotAVAudioPlayer. This means the instance will effectively be leaked.");
    }
    [super setNumberOfLoops: numberOfLoops];
}

@end