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;

static const size_t buffer_size = 1 << 12;

@interface Buffer : NSObject  {
@public
    float left[buffer_size];
    float right[buffer_size];
    NSRange range;
}
@end

@implementation Buffer
@end


@interface AudioFile (){
	ExtAudioFileRef audioFile;
	AudioStreamBasicDescription format;
    NSMutableArray * buffers;
}
- (id)initWithExtAudioFileRef:(ExtAudioFileRef) audioFile;
- (void)setupFormat;
- (Buffer*)getBufferForSample:(NSUInteger) sample;
- (Buffer*)appendBuffer;
@end

@implementation AudioFile

#pragma mark
#pragma mark Creation

- (id)initWithExtAudioFileRef:(ExtAudioFileRef) af{
	if(self = [super init]){
		audioFile = af;
        buffers = [[NSMutableArray alloc] init];
		[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];
}

- (Buffer *)getBufferForSample:(NSUInteger)sample{
    for (Buffer * b in buffers) {
        if(NSLocationInRange(sample, b->range)){
            return b;
        }
    }
    

    while(1){
        Buffer * b = [self appendBuffer];
        if(!b) return nil;
        if(NSLocationInRange(sample, b->range)) return b;
    }
}

- (Buffer *)appendBuffer{
    Buffer * b = [[Buffer alloc] init];
    Buffer * last = [buffers lastObject];
    if(last){
        b->range.location = last->range.location + last->range.length;
    } else {
        b->range.location = 0;
    }
    
    AudioBufferList bufferList;
	bufferList.mNumberBuffers = 1;
	bufferList.mBuffers[0].mNumberChannels = 2;
	bufferList.mBuffers[0].mDataByteSize = buffer_size * format.mBytesPerFrame;
	bufferList.mBuffers[0].mData = calloc(bufferList.mBuffers[0].mDataByteSize, 1);
	
	UInt32 nFrames = buffer_size;
	OSStatus err = ExtAudioFileRead(audioFile, &nFrames, &bufferList);
	assert(err == 0);
	
	short * buffer = bufferList.mBuffers[0].mData;
    
    float * left = b->left;
    float * right = b->right;
	float * leftEnd = left + buffer_size;
	for(unsigned int i = 0; i < nFrames; ++i){
		*left++ = *buffer++ / 32768.0f;
		*right++ = *buffer++ / 32768.0f;
	}
	
	// assume left and right are of the same size
	while(left != leftEnd){
		*left++ = 0;
		*right++ = 0;
	}
    
    b->range.length = nFrames;
	
	free(bufferList.mBuffers[0].mData);
    
    if(!nFrames) return nil;
    [buffers addObject:b];
    return b;
}

#pragma mark
#pragma mark Usage

- (BOOL)fillLeft:(float *)left andRight:(float *)right forRange:(NSRange)range{
    NSUInteger n = range.length;
    
    Buffer * b = nil;
    while ((b = [self getBufferForSample:range.location])) {
        while(range.length && NSLocationInRange(range.location, b->range)){
            *left++ = b->left[range.location - b->range.location];
            *right++ = b->right[range.location - b->range.location];
            range.location++;
            range.length--;
        }
        if(range.length == 0) break;
    }
    
    return range.length < n;
}

@end