/*

     File: MYAudioTapProcessor.m

 Abstract: Audio tap processor using MTAudioProcessingTap for audio visualization and processing.

  Version: 1.0.1

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 */

#import "MYAudioTapProcessor.h"

#import <AVFoundation/AVFoundation.h>

// This struct is used to pass along data between the MTAudioProcessingTap callbacks.

typedef struct AVAudioTapProcessorContext {

    Boolean supportedTapProcessingFormat;

    Boolean isNonInterleaved;

    Float64 sampleRate;

    AudioUnit audioUnit;

    Float64 sampleCount;

    float leftChannelVolume;

    float rightChannelVolume;

    void *self;

} AVAudioTapProcessorContext;

// MTAudioProcessingTap callbacks.

static void tap_InitCallback(MTAudioProcessingTapRef tap, void *clientInfo, void **tapStorageOut);

static void tap_FinalizeCallback(MTAudioProcessingTapRef tap);

static void tap_PrepareCallback(MTAudioProcessingTapRef tap, CMItemCount maxFrames, const AudioStreamBasicDescription *processingFormat);

static void tap_UnprepareCallback(MTAudioProcessingTapRef tap);

static void tap_ProcessCallback(MTAudioProcessingTapRef tap, CMItemCount numberFrames, MTAudioProcessingTapFlags flags, AudioBufferList *bufferListInOut, CMItemCount *numberFramesOut, MTAudioProcessingTapFlags *flagsOut);

// Audio Unit callbacks.

static OSStatus AU_RenderCallback(void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData);

@interface MYAudioTapProcessor ()

{

    AVAudioMix *_audioMix;

}

@end

@implementation MYAudioTapProcessor

- (id)initWithAudioAssetTrack:(AVAssetTrack *)audioAssetTrack

{

    NSParameterAssert(audioAssetTrack && [audioAssetTrack.mediaType isEqualToString:AVMediaTypeAudio]);

    self = [super init];

    if (self)

    {

        _audioAssetTrack = audioAssetTrack;

        _centerFrequency = (4980.0f / 23980.0f); // equals 5000 Hz (assuming sample rate is 48k)

        _bandwidth = (500.0f / 11900.0f); // equals 600 Cents

    }

    return self;

}

#pragma mark - Properties

- (AVAudioMix *)audioMix

{

    if (!_audioMix)

    {

        AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix];

        if (audioMix)

        {

            AVMutableAudioMixInputParameters *audioMixInputParameters = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:self.audioAssetTrack];

            if (audioMixInputParameters)

            {

                MTAudioProcessingTapCallbacks callbacks;

                callbacks.version = kMTAudioProcessingTapCallbacksVersion_0;

                callbacks.clientInfo = (__bridge void *)self,

                callbacks.init = tap_InitCallback;

                callbacks.finalize = tap_FinalizeCallback;

                callbacks.prepare = tap_PrepareCallback;

                callbacks.unprepare = tap_UnprepareCallback;

                callbacks.process = tap_ProcessCallback;

                MTAudioProcessingTapRef audioProcessingTap;

                if (noErr == MTAudioProcessingTapCreate(kCFAllocatorDefault, &callbacks, kMTAudioProcessingTapCreationFlag_PreEffects, &audioProcessingTap))

                {

                    audioMixInputParameters.audioTapProcessor = audioProcessingTap;

                    CFRelease(audioProcessingTap);

                    audioMix.inputParameters = @[audioMixInputParameters];

                    _audioMix = audioMix;

                }

            }

        }

    }

    return _audioMix;

}

- (void)setCenterFrequency:(float)centerFrequency

{

    if (_centerFrequency != centerFrequency)

    {

        _centerFrequency = centerFrequency;

        AVAudioMix *audioMix = self.audioMix;

        if (audioMix)

        {

            // Get pointer to Audio Unit stored in MTAudioProcessingTap context.

            MTAudioProcessingTapRef audioProcessingTap = ((AVMutableAudioMixInputParameters *)audioMix.inputParameters[0]).audioTapProcessor;

            AVAudioTapProcessorContext *context = (AVAudioTapProcessorContext *)MTAudioProcessingTapGetStorage(audioProcessingTap);

            AudioUnit audioUnit = context->audioUnit;

            if (audioUnit)

            {

                // Update center frequency of bandpass filter Audio Unit.

                Float32 newCenterFrequency = (20.0f + ((context->sampleRate * 0.5f) - 20.0f) * self.centerFrequency); // Global, Hz, 20->(SampleRate/2), 5000

                OSStatus status = AudioUnitSetParameter(audioUnit, kBandpassParam_CenterFrequency, kAudioUnitScope_Global, 0, newCenterFrequency, 0);

                if (noErr != status)

                    NSLog(@"AudioUnitSetParameter(kBandpassParam_CenterFrequency): %d", (int)status);

            }

        }

    }

}

- (void)setBandwidth:(float)bandwidth

{

    if (_bandwidth != bandwidth)

    {

        _bandwidth = bandwidth;

        AVAudioMix *audioMix = self.audioMix;

        if (audioMix)

        {

            // Get pointer to Audio Unit stored in MTAudioProcessingTap context.

            MTAudioProcessingTapRef audioProcessingTap = ((AVMutableAudioMixInputParameters *)audioMix.inputParameters[0]).audioTapProcessor;

            AVAudioTapProcessorContext *context = (AVAudioTapProcessorContext *)MTAudioProcessingTapGetStorage(audioProcessingTap);

            AudioUnit audioUnit = context->audioUnit;

            if (audioUnit)

            {

                // Update bandwidth of bandpass filter Audio Unit.

                Float32 newBandwidth = (100.0f + 11900.0f * self.bandwidth);

                OSStatus status = AudioUnitSetParameter(audioUnit, kBandpassParam_Bandwidth, kAudioUnitScope_Global, 0, newBandwidth, 0); // Global, Cents, 100->12000, 600

                if (noErr != status)

                    NSLog(@"AudioUnitSetParameter(kBandpassParam_Bandwidth): %d", (int)status);

            }

        }

    }

}

#pragma mark -

- (void)updateLeftChannelVolume:(float)leftChannelVolume rightChannelVolume:(float)rightChannelVolume

{

    @autoreleasepool

    {

        dispatch_async(dispatch_get_main_queue(), ^{

            // Forward left and right channel volume to delegate.

            if (self.delegate && [self.delegate respondsToSelector:@selector(audioTabProcessor:hasNewLeftChannelValue:rightChannelValue:)])

                [self.delegate audioTabProcessor:self hasNewLeftChannelValue:leftChannelVolume rightChannelValue:rightChannelVolume];

        });

    }

}

@end

#pragma mark - MTAudioProcessingTap Callbacks

static void tap_InitCallback(MTAudioProcessingTapRef tap, void *clientInfo, void **tapStorageOut)

{

    AVAudioTapProcessorContext *context = calloc(1, sizeof(AVAudioTapProcessorContext));

    // Initialize MTAudioProcessingTap context.

    context->supportedTapProcessingFormat = false;

    context->isNonInterleaved = false;

    context->sampleRate = NAN;

    context->audioUnit = NULL;

    context->sampleCount = 0.0f;

    context->leftChannelVolume = 0.0f;

    context->rightChannelVolume = 0.0f;

    context->self = clientInfo;

    *tapStorageOut = context;

}

static void tap_FinalizeCallback(MTAudioProcessingTapRef tap)

{

    AVAudioTapProcessorContext *context = (AVAudioTapProcessorContext *)MTAudioProcessingTapGetStorage(tap);

    // Clear MTAudioProcessingTap context.

    context->self = NULL;

    free(context);

}

static void tap_PrepareCallback(MTAudioProcessingTapRef tap, CMItemCount maxFrames, const AudioStreamBasicDescription *processingFormat)

{

    AVAudioTapProcessorContext *context = (AVAudioTapProcessorContext *)MTAudioProcessingTapGetStorage(tap);

    // Store sample rate for -setCenterFrequency:.

    context->sampleRate = processingFormat->mSampleRate;

    /* Verify processing format (this is not needed for Audio Unit, but for RMS calculation). */

    context->supportedTapProcessingFormat = true;

    if (processingFormat->mFormatID != kAudioFormatLinearPCM)

    {

        NSLog(@"Unsupported audio format ID for audioProcessingTap. LinearPCM only.");

        context->supportedTapProcessingFormat = false;

    }

    if (!(processingFormat->mFormatFlags & kAudioFormatFlagIsFloat))

    {

        NSLog(@"Unsupported audio format flag for audioProcessingTap. Float only.");

        context->supportedTapProcessingFormat = false;

    }

    if (processingFormat->mFormatFlags & kAudioFormatFlagIsNonInterleaved)

    {

        context->isNonInterleaved = true;

    }

    /* Create bandpass filter Audio Unit */

    AudioUnit audioUnit;

    AudioComponentDescription audioComponentDescription;

    audioComponentDescription.componentType = kAudioUnitType_Effect;

    audioComponentDescription.componentSubType = kAudioUnitSubType_BandPassFilter;

    audioComponentDescription.componentManufacturer = kAudioUnitManufacturer_Apple;

    audioComponentDescription.componentFlags = 0;

    audioComponentDescription.componentFlagsMask = 0;

    AudioComponent audioComponent = AudioComponentFindNext(NULL, &audioComponentDescription);

    if (audioComponent)

    {

        if (noErr == AudioComponentInstanceNew(audioComponent, &audioUnit))

        {

            OSStatus status = noErr;

            // Set audio unit input/output stream format to processing format.

            if (noErr == status)

            {

                status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, processingFormat, sizeof(AudioStreamBasicDescription));

            }

            if (noErr == status)

            {

                status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, processingFormat, sizeof(AudioStreamBasicDescription));

            }

            // Set audio unit render callback.

            if (noErr == status)

            {

                AURenderCallbackStruct renderCallbackStruct;

                renderCallbackStruct.inputProc = AU_RenderCallback;

                renderCallbackStruct.inputProcRefCon = (void *)tap;

                status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_SetRenderCallback, kAudioUnitScope_Input, 0, &renderCallbackStruct, sizeof(AURenderCallbackStruct));

            }

            // Set audio unit maximum frames per slice to max frames.

            if (noErr == status)

            {

                UInt32 maximumFramesPerSlice = maxFrames;

                status = AudioUnitSetProperty(audioUnit, kAudioUnitProperty_MaximumFramesPerSlice, kAudioUnitScope_Global, 0, &maximumFramesPerSlice, (UInt32)sizeof(UInt32));

            }

            // Initialize audio unit.

            if (noErr == status)

            {

                status = AudioUnitInitialize(audioUnit);

            }

            if (noErr != status)

            {

                AudioComponentInstanceDispose(audioUnit);

                audioUnit = NULL;

            }

            context->audioUnit = audioUnit;

        }

    }

}

static void tap_UnprepareCallback(MTAudioProcessingTapRef tap)

{

    AVAudioTapProcessorContext *context = (AVAudioTapProcessorContext *)MTAudioProcessingTapGetStorage(tap);

    /* Release bandpass filter Audio Unit */

    if (context->audioUnit)

    {

        AudioUnitUninitialize(context->audioUnit);

        AudioComponentInstanceDispose(context->audioUnit);

        context->audioUnit = NULL;

    }

}

static void tap_ProcessCallback(MTAudioProcessingTapRef tap, CMItemCount numberFrames, MTAudioProcessingTapFlags flags, AudioBufferList *bufferListInOut, CMItemCount *numberFramesOut, MTAudioProcessingTapFlags *flagsOut)

{

    AVAudioTapProcessorContext *context = (AVAudioTapProcessorContext *)MTAudioProcessingTapGetStorage(tap);

    OSStatus status;

    // Skip processing when format not supported.

    if (!context->supportedTapProcessingFormat)

    {

        NSLog(@"Unsupported tap processing format.");

        return;

    }

    MYAudioTapProcessor *self = ((__bridge MYAudioTapProcessor *)context->self);

    if (self.isBandpassFilterEnabled)

    {

        // Apply bandpass filter Audio Unit.

        AudioUnit audioUnit = context->audioUnit;

        if (audioUnit)

        {

            AudioTimeStamp audioTimeStamp;

            audioTimeStamp.mSampleTime = context->sampleCount;

            audioTimeStamp.mFlags = kAudioTimeStampSampleTimeValid;

            status = AudioUnitRender(audioUnit, 0, &audioTimeStamp, 0, (UInt32)numberFrames, bufferListInOut);

            if (noErr != status)

            {

                NSLog(@"AudioUnitRender(): %d", (int)status);

                return;

            }

            // Increment sample count for audio unit.

            context->sampleCount += numberFrames;

            // Set number of frames out.

            *numberFramesOut = numberFrames;

        }

    }

    else

    {

        // Get actual audio buffers from MTAudioProcessingTap (AudioUnitRender() will fill bufferListInOut otherwise).

        status = MTAudioProcessingTapGetSourceAudio(tap, numberFrames, bufferListInOut, flagsOut, NULL, numberFramesOut);

        if (noErr != status)

        {

            NSLog(@"MTAudioProcessingTapGetSourceAudio: %d", (int)status);

            return;

        }

    }

    // Calculate root mean square (RMS) for left and right audio channel.

    for (UInt32 i = 0; i < bufferListInOut->mNumberBuffers; i++)

    {

        AudioBuffer *pBuffer = &bufferListInOut->mBuffers[i];

        UInt32 cSamples = numberFrames * (context->isNonInterleaved ? 1 : pBuffer->mNumberChannels);

        float *pData = (float *)pBuffer->mData;

        float rms = 0.0f;

        for (UInt32 j = 0; j < cSamples; j++)

        {

            rms += pData[j] * pData[j];

        }

        if (cSamples > 0)

        {

            rms = sqrtf(rms / cSamples);

        }

        if (0 == i)

        {

            context->leftChannelVolume = rms;

        }

        if (1 == i || (0 == i && 1 == bufferListInOut->mNumberBuffers))

        {

            context->rightChannelVolume = rms;

        }

    }

    // Pass calculated left and right channel volume to VU meters.

    [self updateLeftChannelVolume:context->leftChannelVolume rightChannelVolume:context->rightChannelVolume];

}

#pragma mark - Audio Unit Callbacks

OSStatus AU_RenderCallback(void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData)

{

    // Just return audio buffers from MTAudioProcessingTap.

    return MTAudioProcessingTapGetSourceAudio(inRefCon, inNumberFrames, ioData, NULL, NULL, NULL);

}