RemoteIO code

// AUGraphSampleViewController.h file

@interface AUGraphSampleViewController : UIViewController {

    AudioComponentDescription mIOUnitDescription; // Initializes it to zero to make sure there are no garbage values
    AUGraph mProcessingGraph;
    AUNode mIONode;
    AudioUnit mIOUnit;

    double mGraphSampleRate;
}

@end


// AUGraphSampleViewController.m file
#import "AUGraphSampleViewController.h"
#import <AudioUnit/AudioUnit.h>
#import <AudioToolbox/AudioToolbox.h>
#import <AVFoundation/AVFoundation.h>

@implementation AUGraphSampleViewController

- (void) printErrorIfAny:(OSStatus)status
{
    if (status == kAUGraphErr_NodeNotFound)
    {
        NSLog(@"Received error : kAUGraphErr_NodeNotFound");
    }
    else if(status == kAUGraphErr_InvalidConnection)
    {
        NSLog(@"Received error : kAUGraphErr_InvalidConnection");
    }
    else if(status == kAUGraphErr_OutputNodeErr)
    {
        NSLog(@"Received error : kAUGraphErr_OutputNodeErr");
    }
    else if(status == kAUGraphErr_CannotDoInCurrentContext)
    {
        NSLog(@"Received error : kAUGraphErr_CannotDoInCurrentContext");
    }
    else if(status == kAUGraphErr_InvalidAudioUnit)
    {
        NSLog(@"Received error : kAUGraphErr_InvalidAudioUnit");
    }
    NSLog(@"%s",(char *)&status);
}

- (void) createAudioUnitDescription
{
    mIOUnitDescription.componentType = kAudioUnitType_Output;
    mIOUnitDescription.componentSubType = kAudioUnitSubType_RemoteIO;
    mIOUnitDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
    mIOUnitDescription.componentFlags = 0;
    mIOUnitDescription.componentFlagsMask = 0;
}

- (void) createInstantiateAndOpenGraph
{

    OSStatus status;
    // Creating a Graph
    status = NewAUGraph(&mProcessingGraph);
    [self printErrorIfAny:status];

    // Intantiating a Graph
    // Add an audio unit node to the graph
    [self createAudioUnitDescription];
    status = AUGraphAddNode(mProcessingGraph, &mIOUnitDescription, &mIONode);
    [self printErrorIfAny:status];

    // Open Graph
    status = AUGraphOpen(mProcessingGraph); // Internally instantiates the audio Unit
    [self printErrorIfAny:status];

    // Obtain reference of the audio units
    AUGraphNodeInfo(mProcessingGraph, mIONode, NULL, &mIOUnit);

    // enable the input
    UInt32 enableInput = 1;
    AudioUnitElement inputBus = 1;
    AudioUnitElement outputBus = 0;
    status = AudioUnitSetProperty(mIOUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, inputBus, &enableInput, sizeof(enableInput));
    [self printErrorIfAny:status];
    status = AudioUnitSetProperty(mIOUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Output, outputBus, &enableInput, sizeof(enableInput));
    [self printErrorIfAny:status];

    // set the output format
    size_t bytesPerSample = sizeof (AudioUnitSampleType);
    AudioStreamBasicDescription stereoStreamFormat = {0};
    stereoStreamFormat.mFormatID = kAudioFormatLinearPCM;
    stereoStreamFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    stereoStreamFormat.mBytesPerPacket  = bytesPerSample;
    stereoStreamFormat.mBytesPerFrame = bytesPerSample;
    stereoStreamFormat.mFramesPerPacket = 1;
    stereoStreamFormat.mBitsPerChannel = 8 * bytesPerSample;
    stereoStreamFormat.mChannelsPerFrame  = 2;  // 1 indicates mono and 2 indicates stereo
    stereoStreamFormat.mSampleRate  = 44100.00;

    status = AudioUnitSetProperty(mIOUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, outputBus, &stereoStreamFormat, sizeof(stereoStreamFormat));
    [self printErrorIfAny:status];
    status = AudioUnitSetProperty(mIOUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, inputBus, &stereoStreamFormat, sizeof(stereoStreamFormat));
    [self printErrorIfAny:status];

    // Initialize the graph
    status = AUGraphInitialize(mProcessingGraph);
    if (status)
    {
        NSLog(@"Error... while initializing the graph");
        [self printErrorIfAny:status];
    }
    else
    {
        NSLog(@"Successfully initialized the graph");
        status = AUGraphStart(mProcessingGraph);
        [self printErrorIfAny:status];
    }
}


/*
// The designated initializer. Override to perform setup that is required before the view is loaded.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}
*/

/*
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView {
}
*/

- (void) printAudioSessionError:(NSError *)error withMsg:(NSString *)msg
{
    if (error)
        NSLog(@"%@ : %@",msg,[error description]);
}

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    [super viewDidLoad];

    // Define the required sample rate
    mGraphSampleRate = 44100.00; // Hertz

    // First set the required Audio Session
    NSError *audioSessionError = nil;
    AVAudioSession *audioSession = [AVAudioSession sharedInstance];
    [audioSession setPreferredHardwareSampleRate:mGraphSampleRate error:&audioSessionError];
    [self printAudioSessionError:audioSessionError withMsg:@"Error while setting hardware sample rate"];
    [audioSession setCategory:AVAudioSessionCategoryPlayAndRecord error:&audioSessionError];    // This category supports Audio input and output.
    [self printAudioSessionError:audioSessionError withMsg:@"Error while setting category"];
    [audioSession setActive:YES error:&audioSessionError];
    [self printAudioSessionError:audioSessionError withMsg:@"Error while activating audio session"];
    mGraphSampleRate = [audioSession currentHardwareSampleRate];    // Reload from system.

    [self createInstantiateAndOpenGraph];
}



/*
// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
*/

- (void)didReceiveMemoryWarning {
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

- (void)viewDidUnload {
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}


- (void)dealloc {
    [super dealloc];
}

@end