Apple

enum : AudioUnitElement {

kOutputElement = 0,

kInputElement = 1

};

const UInt32 disableFlag = 0;

const UInt32 enableFlag = 1;

OSStatus err = noErr;

NSError *error = nil;

// Configure & activate audio session

AVAudioSession *session = [AVAudioSession sharedInstance];

if (![session setCategory:AVAudioSessionCategoryRecord error:&error]) NSLog(@"Error configuring session category: %@", error);

if (![session setMode:AVAudioSessionModeMeasurement error:&error]) NSLog(@"Error configuring session mode: %@", error);

if (![session setActive:YES error:&error]) NSLog(@"Error activating audio session: %@", error);

NSLog(@"Session activated. sample rate %f", session.sampleRate);

NSLog(@"Number of channels %d", session.inputNumberOfChannels);

NSInteger numChannels = session.inputNumberOfChannels;

// Set up Remote I/O audio unit for audio capture

AudioComponent component = AudioComponentFindNext(NULL, &(const AudioComponentDescription){

.componentType = kAudioUnitType_Output,

.componentSubType = kAudioUnitSubType_RemoteIO,

.componentManufacturer = kAudioUnitManufacturer_Apple,

.componentFlags = 0,

.componentFlagsMask = 0

});

AudioComponentInstance unit;

// Create audio component

err = AudioComponentInstanceNew(component, &unit);

if (err != noErr) NSLog(@"Error instantiating audio unit: %@", E2S(err));

// Enable input

err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, kInputElement, &enableFlag, sizeof(enableFlag));

if (err != noErr) NSLog(@"Error enabling input for audio unit: %@", E2S(err));

// Disable output

err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Output, kOutputElement, &disableFlag, sizeof(disableFlag));

if (err != noErr) NSLog(@"Error disabling output for audio unit: %@", E2S(err));

// "The canonical audio sample type for audio units and other audio processing in iPhone OS is noninterleaved linear PCM with 8.24-bit fixed-point samples."

assert(kAudioFormatFlagsAudioUnitCanonical & kAudioFormatFlagIsNonInterleaved);

AudioStreamBasicDescription streamDesc = {

.mSampleRate = session.sampleRate,

.mFormatID = kAudioFormatLinearPCM,

.mFormatFlags = kAudioFormatFlagsAudioUnitCanonical /*matches AudioUnitSampleType*/,

.mBytesPerPacket = sizeof(AudioUnitSampleType) * numChannels,

.mFramesPerPacket = 1,

.mBytesPerFrame = sizeof(AudioUnitSampleType) * numChannels,

.mChannelsPerFrame = numChannels,

.mBitsPerChannel = 8 * sizeof(AudioUnitSampleType),

.mReserved = 0,

};

err = AudioUnitSetProperty(unit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, kOutputElement, &streamDesc, sizeof(streamDesc));

if (err != noErr) NSLog(@"Error configuring input stream format for audio unit: %@", E2S(err));

AURenderCallbackStruct callbacks = {

.inputProc = myInputCallback,

.inputProcRefCon = unit

};

err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Input, kOutputElement, &callbacks, sizeof(callbacks));

if (err != noErr) NSLog(@"Error configuring input callbacks for audio unit: %@", E2S(err));

err = AudioUnitInitialize(unit);

if (err != noErr) NSLog(@"Error initializing audio unit: %@", E2S(err));

err = AudioOutputUnitStart(unit);

if (err != noErr) NSLog(@"Error starting audio unit: %@", E2S(err));