spectogram-prototype/SpectogramPrototype/AudioFile.m

//
//  AudioFile.m
//  SpectogramPrototype
//
//  Created by Joshua Moerman on 28/12/13.
//  Copyright (c) 2013 Joshua Moerman. All rights reserved.
//

#import "AudioFile.h"
#import <AudioToolbox/ExtendedAudioFile.h>

@interface AudioFile (){
	ExtAudioFileRef audioFile;
	AudioStreamBasicDescription format;
}
- (id)initWithExtAudioFileRef:(ExtAudioFileRef) audioFile;
- (void)setupFormat;
@end

@implementation AudioFile

#pragma mark
#pragma mark Creation

- (id)initWithExtAudioFileRef:(ExtAudioFileRef) af{
	if(self = [super init]){
		audioFile = af;
		[self setupFormat];
	}
	return self;
}

- (void)setupFormat{
	format.mSampleRate        = 44100.0f;
	format.mFormatID          = kAudioFormatLinearPCM;
	format.mFormatFlags       = kLinearPCMFormatFlagIsPacked | kLinearPCMFormatFlagIsSignedInteger;
	format.mBytesPerPacket    = 4;
	format.mFramesPerPacket   = 1;
	format.mBytesPerFrame     = 4;
	format.mChannelsPerFrame  = 2;
	format.mBitsPerChannel    = 16;
	format.mReserved          = 0;
	
	UInt32 size = sizeof(format);
	OSStatus err = ExtAudioFileSetProperty(audioFile, kExtAudioFileProperty_ClientDataFormat, size, &format);
	assert(err == 0);
}

- (void)dealloc {
	OSStatus err = ExtAudioFileDispose(audioFile);
	assert(err == 0);
}

+ (AudioFile *)audioFileFromURL:(NSURL *)url{
	ExtAudioFileRef audioFile = NULL;
	OSStatus err = ExtAudioFileOpenURL((__bridge CFURLRef) url, &audioFile);
	assert(err == 0 && audioFile);

	return [[AudioFile alloc] initWithExtAudioFileRef:audioFile];
}

#pragma mark
#pragma mark Usage

- (unsigned int)fillLeft:(float *)left andRight:(float *)right withNumberOfSamples:(unsigned int)nSamples {
	AudioBufferList bufferList;
	bufferList.mNumberBuffers = 1;
	bufferList.mBuffers[0].mNumberChannels = 2;
	bufferList.mBuffers[0].mDataByteSize = nSamples * format.mBytesPerFrame;
	bufferList.mBuffers[0].mData = calloc(bufferList.mBuffers[0].mDataByteSize, 1);
	
	UInt32 nFrames = nSamples;
	OSStatus err = ExtAudioFileRead(audioFile, &nFrames, &bufferList);
	assert(err == 0);
	
	short * buffer = bufferList.mBuffers[0].mData;
	float * leftEnd = left + nSamples;
	for(unsigned int i = 0; i < nFrames; ++i){
		*left++ = *buffer++ / 32768.0;
		*right++ = *buffer++ / 32768.0;
	}
	
	// assume left and right are of the same size
	while(left != leftEnd){
		*left++ = 0.0;
		*right++ = 0.0;
	}
	
	free(bufferList.mBuffers[0].mData);
	
	return nFrames;
}

@end