CLK/OSBindings/Mac/Clock Signal/Wrappers/AudioQueue.m

//
//  AudioQueue.m
//  Clock Signal
//
//  Created by Thomas Harte on 14/01/2016.
//  Copyright © 2016 Thomas Harte. All rights reserved.
//

#import "AudioQueue.h"
@import AudioToolbox;

#define AudioQueueNumAudioBuffers	3
#define AudioQueueStreamLength		2048
#define AudioQueueBufferLength		512

@implementation AudioQueue
{
	AudioQueueRef _audioQueue;
	AudioQueueBufferRef _audioBuffers[AudioQueueNumAudioBuffers];
	unsigned int _audioStreamReadPosition, _audioStreamWritePosition, _queuedAudioStreamSegments;
	int16_t _audioStream[AudioQueueStreamLength];
	BOOL _isOutputtingAudio;
}


#pragma mark -
#pragma mark AudioQueue callbacks and setup; for pushing audio out

- (void)audioQueue:(AudioQueueRef)theAudioQueue didCallbackWithBuffer:(AudioQueueBufferRef)buffer
{
	@synchronized(self)
	{
		if(_queuedAudioStreamSegments > AudioQueueNumAudioBuffers-1) _isOutputtingAudio = YES;

		if(_isOutputtingAudio && _queuedAudioStreamSegments)
		{
			_queuedAudioStreamSegments--;
			memcpy(buffer->mAudioData, &_audioStream[_audioStreamReadPosition], buffer->mAudioDataByteSize);
			_audioStreamReadPosition = (_audioStreamReadPosition + AudioQueueBufferLength)%AudioQueueStreamLength;
		}
		else
		{
			memset(buffer->mAudioData, 0, buffer->mAudioDataByteSize);
			_isOutputtingAudio = NO;
		}
		AudioQueueEnqueueBuffer(theAudioQueue, buffer, 0, NULL);
	}
}

static void audioOutputCallback(
	void *inUserData,
	AudioQueueRef inAQ,
	AudioQueueBufferRef inBuffer)
{
	[(__bridge AudioQueue *)inUserData audioQueue:inAQ didCallbackWithBuffer:inBuffer];
}

- (instancetype)init
{
	self = [super init];

	if(self)
	{
		/*
		
			Describe a mono, 16bit, 44.1Khz audio format
		
		*/
		AudioStreamBasicDescription outputDescription;

		outputDescription.mSampleRate = 44100;

		outputDescription.mFormatID = kAudioFormatLinearPCM;
		outputDescription.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger;

		outputDescription.mBytesPerPacket = 2;
		outputDescription.mFramesPerPacket = 1;
		outputDescription.mBytesPerFrame = 2;
		outputDescription.mChannelsPerFrame = 1;
		outputDescription.mBitsPerChannel = 16;

		outputDescription.mReserved = 0;

		// create an audio output queue along those lines
		if(!AudioQueueNewOutput(
			&outputDescription,
			audioOutputCallback,
			(__bridge void *)(self),
			NULL,
			kCFRunLoopCommonModes,
			0,
			&_audioQueue))
		{
			_audioStreamWritePosition = AudioQueueBufferLength;
			UInt32 bufferBytes = AudioQueueBufferLength * sizeof(int16_t);

			int c = AudioQueueNumAudioBuffers;
			while(c--)
			{
				AudioQueueAllocateBuffer(_audioQueue, bufferBytes, &_audioBuffers[c]);
				memset(_audioBuffers[c]->mAudioData, 0, bufferBytes);
				_audioBuffers[c]->mAudioDataByteSize = bufferBytes;
				AudioQueueEnqueueBuffer(_audioQueue, _audioBuffers[c], 0, NULL);
			}

			AudioQueueStart(_audioQueue, NULL);
		}
	}

	return self;
}

- (void)dealloc
{
	if(_audioQueue) AudioQueueDispose(_audioQueue, NO);
}

- (void)enqueueAudioBuffer:(const int16_t *)buffer numberOfSamples:(unsigned int)lengthInSamples
{
	@synchronized(self)
	{
		memcpy(&_audioStream[_audioStreamWritePosition], buffer, lengthInSamples * sizeof(int16_t));
		_audioStreamWritePosition = (_audioStreamWritePosition + lengthInSamples)%AudioQueueStreamLength;

		if(_queuedAudioStreamSegments == (AudioQueueStreamLength/AudioQueueBufferLength))
		{
			_audioStreamReadPosition = (_audioStreamReadPosition + lengthInSamples)%AudioQueueStreamLength;
		}
		else
		{
			_queuedAudioStreamSegments++;
		}
	}
}

@end