ExtAudioFileRef sourceFile = 0;

ExtAudioFileRef destinationFile = 0;

OSStatus error = noErr;

AudioStreamBasicDescription srcFormat, destFormat;

UInt32 size = sizeof(srcFormat);

error = ExtAudioFileOpenURL((CFURLRef)self.track.location, &sourceFile);

if(error != noErr)

NSLog(@"conversion error: %i", error);

error = noErr;

ExtAudioFileGetProperty(sourceFile, kExtAudioFileProperty_FileDataFormat, &size, &srcFormat);

destFormat.mFormatID = kAudioFormatMPEG4AAC;

destFormat.mSampleRate = 22000;

destFormat.mFormatFlags = 0;

destFormat.mBytesPerPacket = 2; // must have a value or won't write apparently

destFormat.mFramesPerPacket = 0;

destFormat.mBytesPerFrame = 0;

destFormat.mChannelsPerFrame = 1;

destFormat.mBitsPerChannel = 0;

destFormat.mReserved = 0;

//create the output file

NSString *destURL = [self.track.location absoluteString];

NSLog(@"source url: %@", destURL);

destURL = [destURL substringToIndex:([destURL length] - 3)]; //remove caf extension

NSLog(@"source url with no extension: %@", destURL);

destURL = [NSString stringWithFormat:@"%@m4a",destURL]; //add acc extension

NSLog(@"dest url with correct extension: %@", destURL);

NSURL *destinationURL = [NSURL URLWithString:destURL];

size = sizeof(destFormat);

AudioFormatGetProperty(kAudioFormatProperty_FormatInfo, 0, nil, &size, &destFormat);

error = ExtAudioFileCreateWithURL((CFURLRef)destinationURL, kAudioFileM4AType, &destFormat, NULL, kAudioFileFlags_EraseFile, &destinationFile);

if(error != noErr)

NSLog(@"conversion error: %i", error);

error = noErr;

//canonical format

AudioStreamBasicDescription clientFormat;

clientFormat.mFormatID = kAudioFormatLinearPCM;

clientFormat.mSampleRate = 22000;

int sampleSize = sizeof(AudioSampleType);

clientFormat.mFormatFlags = kAudioFormatFlagsCanonical;

clientFormat.mBitsPerChannel = 8 * sampleSize;

clientFormat.mChannelsPerFrame = 1;

clientFormat.mFramesPerPacket = 1;

clientFormat.mBytesPerPacket = sampleSize;

clientFormat.mBytesPerFrame = sampleSize;

clientFormat.mFormatFlags |= kAudioFormatFlagIsNonInterleaved;

//set the intermediate format to canonical on the source file for conversion (?)

ExtAudioFileSetProperty(sourceFile, kExtAudioFileProperty_ClientDataFormat, size, &clientFormat);

//get the converter

AudioConverterRef audioConverter;

size = sizeof(audioConverter);

error = ExtAudioFileGetProperty(destinationFile, kExtAudioFileProperty_AudioConverter, &size, &audioConverter);

if(error != noErr)

NSLog(@"error getting converter: %i", error);

error = noErr;

/*UInt32 bitRate = 64000;

error = AudioConverterSetProperty(audioConverter, kAudioConverterEncodeBitRate, sizeof(bitRate), &bitRate);

if(error != noErr)

NSLog(@"error setting bit rate: %i", error);

error = noErr;*/

// set up buffers

UInt32 bufferByteSize = 32768;

char srcBuffer[bufferByteSize];

NSLog(@"converting...");

int i=0;

while (true) {

i++;

AudioBufferList fillBufList;

fillBufList.mNumberBuffers = 1;

fillBufList.mBuffers[0].mNumberChannels = 1;

fillBufList.mBuffers[0].mDataByteSize = bufferByteSize;

fillBufList.mBuffers[0].mData = srcBuffer;

// client format is always linear PCM - so here we determine how many frames of lpcm

// we can read/write given our buffer size

UInt32 numFrames = bufferByteSize / clientFormat.mBytesPerFrame;

error = ExtAudioFileRead(sourceFile, &numFrames, &fillBufList);

if(error != noErr)

NSLog(@"read error: %i run: %i", error, i);

if (!numFrames) {

// this is our termination condition

error = noErr;

break;

}

//this is the actual conversion

error = ExtAudioFileWrite(destinationFile, numFrames, &fillBufList);

if(error != noErr)

NSLog(@"conversion error: %i run: %i", error, i);

}

if (destinationFile) ExtAudioFileDispose(destinationFile);

if (sourceFile) ExtAudioFileDispose(sourceFile);