Help with AudioQueueServices!

[AnotherJake]

A quick glance at the SDL source code suggests to me that they're using RemoteIO.

Figuring out RemoteIO is not particularly easy because, again as usual, the documentation is nearly non-existent or rather poor -- at least the last time I looked. I put together a tiny demo to maybe get you started. Make a new OpenGL ES app from the template in Xcode. Add the AudioToolbox framework to the project. Then copy the code below and paste it over what's in the <myAppName>AppDelegate.m file. I called mine iPhoneAUTest, so it wound up being iPhoneAUTestAppDelegate.m. You can simply change that to whatever you want. Here's the code:

#import "iPhoneAUTestAppDelegate.h"
#import "EAGLView.h"
#import <AudioUnit/AudioUnit.h>

static bool			silent = false;
static float		volume = 0.25f;
static AudioUnit	audioUnit;

static void RenderAudio(void *left, void *right, unsigned numSamples, unsigned dataSize)
{
	// early out
	if (silent)
	{
		memset(left, 0, dataSize);
		memset(right, 0, dataSize);
		return;
	}
	
	// do something like this to generate your own audio
	unsigned i;
	for (i = 0; i < numSamples; i++)
	{
		// do a cheesy sine wave in the left channel so we have something to hear,
		// and just copy it over to the right channel for demonstration
		static unsigned long sampleIndex = 0;
		float myFloatSampleLeft = sinf((float)sampleIndex++ * 0.1f) * volume;
		float myFloatSampleRight = myFloatSampleLeft;
		
		// output your audio here, in this case, sample by sample, converting from float to int
		((AudioSampleType *)left)[i] = (AudioSampleType)(myFloatSampleLeft * 32000.0f);
		((AudioSampleType *)right)[i] = (AudioSampleType)(myFloatSampleRight * 32000.0f);
	}
	
	/*
		do something like this instead for decoding audio using some codec
	
	for (i = 0; i < numSamples; i++)
	{
		if (myStreamIndex >= myNumSamplesInBuffer)
			myDecodeAnotherBufferWorthOfSamples();
		
		// could do memcpy from your buffer here instead for better efficiency
		((AudioSampleType *)left)[i] = (AudioSampleType)myBuffer[myStreamIndex++]];
		((AudioSampleType *)right)[i] = (AudioSampleType)myBuffer[myStreamIndex++]];
	}*/
}

static OSStatus AudioOutputCallback(void *inRefCon,
                                  AudioUnitRenderActionFlags *ioActionFlags,
                                  const AudioTimeStamp *inTimeStamp,
                                  UInt32 inBusNumber,
                                  UInt32 inNumberFrames,
                                  AudioBufferList *ioData)
{
	unsigned	dataSize = ioData->mBuffers[0].mDataByteSize;
	unsigned	numSamples = dataSize / sizeof(AudioSampleType); // 16-bit
	
	RenderAudio(ioData->mBuffers[0].mData, ioData->mBuffers[1].mData, numSamples, dataSize);
    return noErr;
}

static void DisableAudioOutputiPhone(void)
{
	AudioOutputUnitStop(audioUnit);
	
	AURenderCallbackStruct		callback;
	callback.inputProc = NULL;
	callback.inputProcRefCon = NULL;
	AudioUnitSetProperty(audioUnit,
						kAudioUnitProperty_SetRenderCallback,
						kAudioUnitScope_Global,
						0,
						&callback,
						sizeof(AURenderCallbackStruct));
	
	AudioUnitUninitialize(audioUnit);
	AudioComponentInstanceDispose(audioUnit);
}

static void EnableAudioOutputiPhone(void)
{
	OSStatus					status;
	AudioStreamBasicDescription	audioFormat;
	AudioComponentDescription	desc;
	
	desc.componentType = kAudioUnitType_Output;
	desc.componentSubType = kAudioUnitSubType_RemoteIO;
	desc.componentFlags = 0;
	desc.componentFlagsMask = 0;
	desc.componentManufacturer = kAudioUnitManufacturer_Apple;
	AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);
	status = AudioComponentInstanceNew(inputComponent, &audioUnit);
	UInt32 flag = 1;
	status = AudioUnitSetProperty(audioUnit, 
								  kAudioOutputUnitProperty_EnableIO, 
								  kAudioUnitScope_Output, 
								  0,
								  &flag, 
								  sizeof(flag));
	
	// 16-bit int output
	//audioFormat.mSampleRate = 44100.0;
	audioFormat.mSampleRate = 22050.0;
	audioFormat.mFormatID = kAudioFormatLinearPCM;
	audioFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
	audioFormat.mFormatFlags |= kAudioFormatFlagIsNonInterleaved; // split into left/right for the callback
	UInt32 sampleSize = sizeof(AudioSampleType); // 16-bit signed int
	audioFormat.mBytesPerPacket = sampleSize;
	audioFormat.mFramesPerPacket = 1;
	audioFormat.mBytesPerFrame = sampleSize;
	audioFormat.mChannelsPerFrame = 2;
	audioFormat.mBitsPerChannel = 8 * sampleSize;
	
	status = AudioUnitSetProperty(audioUnit, 
								  kAudioUnitProperty_StreamFormat, 
								  kAudioUnitScope_Input, 
								  0, 
								  &audioFormat, 
								  sizeof(audioFormat));
	 
	AURenderCallbackStruct	callbackStruct;
	callbackStruct.inputProc = AudioOutputCallback;
	callbackStruct.inputProcRefCon = NULL;
	status = AudioUnitSetProperty(audioUnit, 
								  kAudioUnitProperty_SetRenderCallback, 
								  kAudioUnitScope_Global, 
								  0,
								  &callbackStruct, 
								  sizeof(callbackStruct));
	
	status = AudioUnitInitialize(audioUnit);
	if (status != noErr)
	{
		printf("%s ERROR: AudioUnitInitialize failed\n", __FUNCTION__);
	}
	
	AudioOutputUnitStart(audioUnit);
}

@implementation iPhoneAUTestAppDelegate

@synthesize window;
@synthesize glView;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
	EnableAudioOutputiPhone();
    [glView startAnimation];
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
    [glView stopAnimation];
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    [glView startAnimation];
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    [glView stopAnimation];
}

- (void)dealloc
{
    [window release];
    [glView release];

    [super dealloc];
}

@end