Music to spectrogram on iOS with the accelerate framework
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//
// 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;
@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++ / 32768.0f;
*right++ = *buffer++ / 32768.0f;
}
// assume left and right are of the same size
while(left != leftEnd){
*left++ = 0;
*right++ = 0;
}
free(bufferList.mBuffers[0].mData);
return nFrames;
}
@end