Carla/source/modules/juce_audio_devices/native/juce_ios_Audio.cpp

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2016 - ROLI Ltd.

   Permission is granted to use this software under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license/

   Permission to use, copy, modify, and/or distribute this software for any
   purpose with or without fee is hereby granted, provided that the above
   copyright notice and this permission notice appear in all copies.

   THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH REGARD
   TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
   FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT,
   OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
   USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
   TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
   OF THIS SOFTWARE.

   -----------------------------------------------------------------------------

   To release a closed-source product which uses other parts of JUCE not
   licensed under the ISC terms, commercial licenses are available: visit
   www.juce.com for more information.

  ==============================================================================
*/

class iOSAudioIODevice;

static const char* const iOSAudioDeviceName = "iOS Audio";

//==============================================================================
struct AudioSessionHolder
{
    AudioSessionHolder();
    ~AudioSessionHolder();

    void handleStatusChange (bool enabled, const char* reason) const;
    void handleRouteChange (const char* reason) const;

    Array<iOSAudioIODevice*> activeDevices;

    id nativeSession;
};

static const char* getRoutingChangeReason (AVAudioSessionRouteChangeReason reason) noexcept
{
    switch (reason)
    {
        case AVAudioSessionRouteChangeReasonNewDeviceAvailable:         return "New device available";
        case AVAudioSessionRouteChangeReasonOldDeviceUnavailable:       return "Old device unavailable";
        case AVAudioSessionRouteChangeReasonCategoryChange:             return "Category change";
        case AVAudioSessionRouteChangeReasonOverride:                   return "Override";
        case AVAudioSessionRouteChangeReasonWakeFromSleep:              return "Wake from sleep";
        case AVAudioSessionRouteChangeReasonNoSuitableRouteForCategory: return "No suitable route for category";
        case AVAudioSessionRouteChangeReasonRouteConfigurationChange:   return "Route configuration change";
        case AVAudioSessionRouteChangeReasonUnknown:
        default:                                                        return "Unknown";
    }
}

bool getNotificationValueForKey (NSNotification* notification, NSString* key, NSUInteger& value) noexcept
{
    if (notification != nil)
    {
        if (NSDictionary* userInfo = [notification userInfo])
        {
            if (NSNumber* number = [userInfo objectForKey: key])
            {
                value = [number unsignedIntegerValue];
                return true;
            }
        }
    }

    jassertfalse;
    return false;
}

} // juce namespace

//==============================================================================
@interface iOSAudioSessionNative  : NSObject
{
@private
    juce::AudioSessionHolder* audioSessionHolder;
};

- (id) init: (juce::AudioSessionHolder*) holder;
- (void) dealloc;

- (void) audioSessionChangedInterruptionType: (NSNotification*) notification;
- (void) handleMediaServicesReset;
- (void) handleMediaServicesLost;
- (void) handleRouteChange: (NSNotification*) notification;
@end

@implementation iOSAudioSessionNative

- (id) init: (juce::AudioSessionHolder*) holder
{
    self = [super init];

    if (self != nil)
    {
        audioSessionHolder = holder;

        auto session = [AVAudioSession sharedInstance];
        auto centre = [NSNotificationCenter defaultCenter];

        [centre addObserver: self
                   selector: @selector (audioSessionChangedInterruptionType:)
                       name: AVAudioSessionInterruptionNotification
                     object: session];

        [centre addObserver: self
                   selector: @selector (handleMediaServicesLost)
                       name: AVAudioSessionMediaServicesWereLostNotification
                     object: session];

        [centre addObserver: self
                   selector: @selector (handleMediaServicesReset)
                       name: AVAudioSessionMediaServicesWereResetNotification
                     object: session];

        [centre addObserver: self
                   selector: @selector (handleRouteChange:)
                       name: AVAudioSessionRouteChangeNotification
                     object: session];
    }
    else
    {
        jassertfalse;
    }

    return self;
}

- (void) dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver: self];
    [super dealloc];
}

- (void) audioSessionChangedInterruptionType: (NSNotification*) notification
{
    NSUInteger value;

    if (juce::getNotificationValueForKey (notification, AVAudioSessionInterruptionTypeKey, value))
    {
        switch ((AVAudioSessionInterruptionType) value)
        {
            case AVAudioSessionInterruptionTypeBegan:
                audioSessionHolder->handleStatusChange (false, "AVAudioSessionInterruptionTypeBegan");
                break;

            case AVAudioSessionInterruptionTypeEnded:
                audioSessionHolder->handleStatusChange (true, "AVAudioSessionInterruptionTypeEnded");
                break;

            // No default so the code doesn't compile if this enum is extended.
        }
    }
}

- (void) handleMediaServicesReset
{
    audioSessionHolder->handleStatusChange (true, "AVAudioSessionMediaServicesWereResetNotification");
}

- (void) handleMediaServicesLost
{
    audioSessionHolder->handleStatusChange (false, "AVAudioSessionMediaServicesWereLostNotification");
}

- (void) handleRouteChange: (NSNotification*) notification
{
    NSUInteger value;

    if (juce::getNotificationValueForKey (notification, AVAudioSessionRouteChangeReasonKey, value))
        audioSessionHolder->handleRouteChange (juce::getRoutingChangeReason ((AVAudioSessionRouteChangeReason) value));
}

@end

//==============================================================================
namespace juce {

#ifndef JUCE_IOS_AUDIO_LOGGING
 #define JUCE_IOS_AUDIO_LOGGING 0
#endif

#if JUCE_IOS_AUDIO_LOGGING
 #define JUCE_IOS_AUDIO_LOG(x)  DBG(x)
#else
 #define JUCE_IOS_AUDIO_LOG(x)
#endif

static void logNSError (NSError* e)
{
    if (e != nil)
    {
        JUCE_IOS_AUDIO_LOG ("iOS Audio error: " << [e.localizedDescription UTF8String]);
        jassertfalse;
    }
}

#define JUCE_NSERROR_CHECK(X)     { NSError* error = nil; X; logNSError (error); }


//==============================================================================
class iOSAudioIODevice  : public AudioIODevice
{
public:
    iOSAudioIODevice (const String& deviceName)
        : AudioIODevice (deviceName, iOSAudioDeviceName)
    {
        sessionHolder->activeDevices.add (this);
        updateSampleRateAndAudioInput();
    }

    ~iOSAudioIODevice()
    {
        sessionHolder->activeDevices.removeFirstMatchingValue (this);
        close();
    }

    StringArray getOutputChannelNames() override
    {
        return { "Left", "Right" };
    }

    StringArray getInputChannelNames() override
    {
        if (audioInputIsAvailable)
            return { "Left", "Right" };

        return {};
    }

    static void setAudioSessionActive (bool enabled)
    {
        JUCE_NSERROR_CHECK ([[AVAudioSession sharedInstance] setActive: enabled
                                                                 error: &error]);
    }

    static double trySampleRate (double rate)
    {
        auto session = [AVAudioSession sharedInstance];
        JUCE_NSERROR_CHECK ([session setPreferredSampleRate: rate
                                                      error: &error]);
        return session.sampleRate;
    }

    Array<double> getAvailableSampleRates() override
    {
        Array<double> rates;

        // Important: the supported audio sample rates change on the iPhone 6S
        // depending on whether the headphones are plugged in or not!
        setAudioSessionActive (true);

        AudioUnitRemovePropertyListenerWithUserData (audioUnit,
                                                     kAudioUnitProperty_StreamFormat,
                                                     handleStreamFormatChangeCallback,
                                                     this);

        const double lowestRate = trySampleRate (4000);
        const double highestRate = trySampleRate (192000);

        for (double rate = lowestRate; rate <= highestRate; rate += 1000)
        {
            const double supportedRate = trySampleRate (rate);

            rates.addIfNotAlreadyThere (supportedRate);
            rate = jmax (rate, supportedRate);
        }

        trySampleRate (getCurrentSampleRate());

        AudioUnitAddPropertyListener (audioUnit,
                                      kAudioUnitProperty_StreamFormat,
                                      handleStreamFormatChangeCallback,
                                      this);

        for (auto r : rates)
        {
            ignoreUnused (r);
            JUCE_IOS_AUDIO_LOG ("available rate = " + String (r, 0) + "Hz");
        }

        return rates;
    }

    Array<int> getAvailableBufferSizes() override
    {
        Array<int> r;

        for (int i = 6; i < 13; ++i)
            r.add (1 << i);

        return r;
    }

    int getDefaultBufferSize() override
    {
       #if TARGET_IPHONE_SIMULATOR
        return 512;
       #else
        return 256;
       #endif
    }

    String open (const BigInteger& inputChannelsWanted,
                 const BigInteger& outputChannelsWanted,
                 double targetSampleRate, int bufferSize) override
    {
        close();

        lastError.clear();
        preferredBufferSize = bufferSize <= 0 ? getDefaultBufferSize()
                                              : bufferSize;

        //  xxx set up channel mapping

        activeOutputChans = outputChannelsWanted;
        activeOutputChans.setRange (2, activeOutputChans.getHighestBit(), false);
        numOutputChannels = activeOutputChans.countNumberOfSetBits();
        monoOutputChannelNumber = activeOutputChans.findNextSetBit (0);

        activeInputChans = inputChannelsWanted;
        activeInputChans.setRange (2, activeInputChans.getHighestBit(), false);
        numInputChannels = activeInputChans.countNumberOfSetBits();
        monoInputChannelNumber = activeInputChans.findNextSetBit (0);

        setAudioSessionActive (true);

        // Set the session category & options:
        auto session = [AVAudioSession sharedInstance];

        const bool useInputs = (numInputChannels > 0 && audioInputIsAvailable);

        NSString* category = (useInputs ? AVAudioSessionCategoryPlayAndRecord : AVAudioSessionCategoryPlayback);

        NSUInteger options = AVAudioSessionCategoryOptionMixWithOthers; // Alternatively AVAudioSessionCategoryOptionDuckOthers
        if (useInputs) // These options are only valid for category = PlayAndRecord
            options |= (AVAudioSessionCategoryOptionDefaultToSpeaker | AVAudioSessionCategoryOptionAllowBluetooth);

        JUCE_NSERROR_CHECK ([session setCategory: category
                                     withOptions: options
                                           error: &error]);

        fixAudioRouteIfSetToReceiver();

        // Set the sample rate
        trySampleRate (targetSampleRate);
        updateSampleRateAndAudioInput();
        updateCurrentBufferSize();

        prepareFloatBuffers (actualBufferSize);

        isRunning = true;
        handleRouteChange ("Started AudioUnit");

        lastError = (audioUnit != 0 ? "" : "Couldn't open the device");

        setAudioSessionActive (true);

        return lastError;
    }

    void close() override
    {
        if (isRunning)
        {
            isRunning = false;

            if (audioUnit != 0)
            {
                AudioOutputUnitStart (audioUnit);
                AudioComponentInstanceDispose (audioUnit);
                audioUnit = 0;
            }

            setAudioSessionActive (false);
        }
    }

    bool isOpen() override                      { return isRunning; }

    int getCurrentBufferSizeSamples() override  { return actualBufferSize; }
    double getCurrentSampleRate() override      { return sampleRate; }
    int getCurrentBitDepth() override           { return 16; }

    BigInteger getActiveOutputChannels() const override    { return activeOutputChans; }
    BigInteger getActiveInputChannels() const override     { return activeInputChans; }

    int getOutputLatencyInSamples() override    { return roundToInt (getCurrentSampleRate() * [AVAudioSession sharedInstance].outputLatency); }
    int getInputLatencyInSamples()  override    { return roundToInt (getCurrentSampleRate() * [AVAudioSession sharedInstance].inputLatency); }

    void start (AudioIODeviceCallback* newCallback) override
    {
        if (isRunning && callback != newCallback)
        {
            if (newCallback != nullptr)
                newCallback->audioDeviceAboutToStart (this);

            const ScopedLock sl (callbackLock);
            callback = newCallback;
        }
    }

    void stop() override
    {
        if (isRunning)
        {
            AudioIODeviceCallback* lastCallback;

            {
                const ScopedLock sl (callbackLock);
                lastCallback = callback;
                callback = nullptr;
            }

            if (lastCallback != nullptr)
                lastCallback->audioDeviceStopped();
        }
    }

    bool isPlaying() override            { return isRunning && callback != nullptr; }
    String getLastError() override       { return lastError; }

    bool setAudioPreprocessingEnabled (bool enable) override
    {
        auto session = [AVAudioSession sharedInstance];

        NSString* mode = (enable ? AVAudioSessionModeMeasurement
                                 : AVAudioSessionModeDefault);

        JUCE_NSERROR_CHECK ([session setMode: mode
                                       error: &error]);

        return session.mode == mode;
    }

    void invokeAudioDeviceErrorCallback (const String& reason)
    {
        const ScopedLock sl (callbackLock);

        if (callback != nullptr)
            callback->audioDeviceError (reason);
    }

    void handleStatusChange (bool enabled, const char* reason)
    {
        const ScopedLock myScopedLock (callbackLock);

        JUCE_IOS_AUDIO_LOG ("handleStatusChange: enabled: " << (int) enabled << ", reason: " << reason);

        isRunning = enabled;
        setAudioSessionActive (enabled);

        if (enabled)
            AudioOutputUnitStart (audioUnit);
        else
            AudioOutputUnitStop (audioUnit);

        if (! enabled)
            invokeAudioDeviceErrorCallback (reason);
    }

    void handleRouteChange (const char* reason)
    {
        const ScopedLock myScopedLock (callbackLock);

        JUCE_IOS_AUDIO_LOG ("handleRouteChange: reason: " << reason);

        fixAudioRouteIfSetToReceiver();

        if (isRunning)
        {
            invokeAudioDeviceErrorCallback (reason);
            updateSampleRateAndAudioInput();
            updateCurrentBufferSize();
            createAudioUnit();

            setAudioSessionActive (true);

            if (audioUnit != 0)
            {
                UInt32 formatSize = sizeof (format);
                AudioUnitGetProperty (audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 1, &format, &formatSize);
                AudioOutputUnitStart (audioUnit);
            }

            if (callback != nullptr)
            {
                callback->audioDeviceStopped();
                callback->audioDeviceAboutToStart (this);
            }
        }
    }

private:
    //==============================================================================
    SharedResourcePointer<AudioSessionHolder> sessionHolder;
    CriticalSection callbackLock;
    NSTimeInterval sampleRate = 0;
    int numInputChannels = 2, numOutputChannels = 2;
    int preferredBufferSize = 0, actualBufferSize = 0;
    bool isRunning = false;
    String lastError;

    AudioStreamBasicDescription format;
    AudioUnit audioUnit {};
    bool audioInputIsAvailable = false;
    AudioIODeviceCallback* callback = nullptr;
    BigInteger activeOutputChans, activeInputChans;

    AudioSampleBuffer floatData;
    float* inputChannels[3];
    float* outputChannels[3];
    bool monoInputChannelNumber, monoOutputChannelNumber;

    void prepareFloatBuffers (int bufferSize)
    {
        if (numInputChannels + numOutputChannels > 0)
        {
            floatData.setSize (numInputChannels + numOutputChannels, bufferSize);
            zeromem (inputChannels, sizeof (inputChannels));
            zeromem (outputChannels, sizeof (outputChannels));

            for (int i = 0; i < numInputChannels; ++i)
                inputChannels[i] = floatData.getWritePointer (i);

            for (int i = 0; i < numOutputChannels; ++i)
                outputChannels[i] = floatData.getWritePointer (i + numInputChannels);
        }
    }

    //==============================================================================
    OSStatus process (AudioUnitRenderActionFlags* flags, const AudioTimeStamp* time,
                      const UInt32 numFrames, AudioBufferList* data)
    {
        OSStatus err = noErr;

        if (audioInputIsAvailable && numInputChannels > 0)
            err = AudioUnitRender (audioUnit, flags, time, 1, numFrames, data);

        const ScopedTryLock stl (callbackLock);

        if (stl.isLocked() && callback != nullptr)
        {
            if ((int) numFrames > floatData.getNumSamples())
                prepareFloatBuffers ((int) numFrames);

            if (audioInputIsAvailable && numInputChannels > 0)
            {
                short* shortData = (short*) data->mBuffers[0].mData;

                if (numInputChannels >= 2)
                {
                    for (UInt32 i = 0; i < numFrames; ++i)
                    {
                        inputChannels[0][i] = *shortData++ * (1.0f / 32768.0f);
                        inputChannels[1][i] = *shortData++ * (1.0f / 32768.0f);
                    }
                }
                else
                {
                    if (monoInputChannelNumber > 0)
                        ++shortData;

                    for (UInt32 i = 0; i < numFrames; ++i)
                    {
                        inputChannels[0][i] = *shortData++ * (1.0f / 32768.0f);
                        ++shortData;
                    }
                }
            }
            else
            {
                for (int i = numInputChannels; --i >= 0;)
                    zeromem (inputChannels[i], sizeof (float) * numFrames);
            }

            callback->audioDeviceIOCallback ((const float**) inputChannels, numInputChannels,
                                             outputChannels, numOutputChannels, (int) numFrames);

            short* const shortData = (short*) data->mBuffers[0].mData;
            int n = 0;

            if (numOutputChannels >= 2)
            {
                for (UInt32 i = 0; i < numFrames; ++i)
                {
                    shortData [n++] = (short) (outputChannels[0][i] * 32767.0f);
                    shortData [n++] = (short) (outputChannels[1][i] * 32767.0f);
                }
            }
            else if (numOutputChannels == 1)
            {
                for (UInt32 i = 0; i < numFrames; ++i)
                {
                    const short s = (short) (outputChannels[monoOutputChannelNumber][i] * 32767.0f);
                    shortData [n++] = s;
                    shortData [n++] = s;
                }
            }
            else
            {
                zeromem (data->mBuffers[0].mData, 2 * sizeof (short) * numFrames);
            }
        }
        else
        {
            zeromem (data->mBuffers[0].mData, 2 * sizeof (short) * numFrames);
        }

        return err;
    }

    void updateSampleRateAndAudioInput()
    {
        auto session = [AVAudioSession sharedInstance];
        sampleRate = session.sampleRate;
        audioInputIsAvailable = session.isInputAvailable;
        actualBufferSize = roundToInt (sampleRate * session.IOBufferDuration);

        JUCE_IOS_AUDIO_LOG ("AVAudioSession: sampleRate: " << sampleRate
                             << " Hz, audioInputAvailable: " << (int) audioInputIsAvailable
                             << ", buffer size: " << actualBufferSize);
    }

    void updateCurrentBufferSize()
    {
        NSTimeInterval bufferDuration = sampleRate > 0 ? (NSTimeInterval) ((preferredBufferSize + 1) / sampleRate) : 0.0;

        JUCE_NSERROR_CHECK ([[AVAudioSession sharedInstance] setPreferredIOBufferDuration: bufferDuration
                                                                                    error: &error]);
        updateSampleRateAndAudioInput();
    }

    //==============================================================================
    static OSStatus processStatic (void* client, AudioUnitRenderActionFlags* flags, const AudioTimeStamp* time,
                                   UInt32 /*busNumber*/, UInt32 numFrames, AudioBufferList* data)
    {

        return static_cast<iOSAudioIODevice*> (client)->process (flags, time, numFrames, data);
    }

    //==============================================================================
    void resetFormat (const int numChannels) noexcept
    {
        zerostruct (format);
        format.mFormatID = kAudioFormatLinearPCM;
        format.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked | kAudioFormatFlagsNativeEndian;
        format.mBitsPerChannel = 8 * sizeof (short);
        format.mChannelsPerFrame = (UInt32) numChannels;
        format.mFramesPerPacket = 1;
        format.mBytesPerFrame = format.mBytesPerPacket = (UInt32) numChannels * sizeof (short);
    }

    bool createAudioUnit()
    {
        if (audioUnit != 0)
        {
            AudioComponentInstanceDispose (audioUnit);
            audioUnit = 0;
        }

        resetFormat (2);

        AudioComponentDescription desc;
        desc.componentType = kAudioUnitType_Output;
        desc.componentSubType = kAudioUnitSubType_RemoteIO;
        desc.componentManufacturer = kAudioUnitManufacturer_Apple;
        desc.componentFlags = 0;
        desc.componentFlagsMask = 0;

        AudioComponent comp = AudioComponentFindNext (0, &desc);
        AudioComponentInstanceNew (comp, &audioUnit);

        if (audioUnit == 0)
            return false;

        if (numInputChannels > 0)
        {
            const UInt32 one = 1;
            AudioUnitSetProperty (audioUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, 1, &one, sizeof (one));
        }

        {
            AudioChannelLayout layout;
            layout.mChannelBitmap = 0;
            layout.mNumberChannelDescriptions = 0;
            layout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
            AudioUnitSetProperty (audioUnit, kAudioUnitProperty_AudioChannelLayout, kAudioUnitScope_Input,  0, &layout, sizeof (layout));
            AudioUnitSetProperty (audioUnit, kAudioUnitProperty_AudioChannelLayout, kAudioUnitScope_Output, 0, &layout, sizeof (layout));
        }

        {
            AURenderCallbackStruct inputProc;
            inputProc.inputProc = processStatic;
            inputProc.inputProcRefCon = this;
            AudioUnitSetProperty (audioUnit, kAudioUnitProperty_SetRenderCallback, kAudioUnitScope_Input, 0, &inputProc, sizeof (inputProc));
        }

        AudioUnitSetProperty (audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input,  0, &format, sizeof (format));
        AudioUnitSetProperty (audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 1, &format, sizeof (format));

        UInt32 framesPerSlice;
        UInt32 dataSize = sizeof (framesPerSlice);

        AudioUnitInitialize (audioUnit);

        updateCurrentBufferSize();

        if (AudioUnitGetProperty (audioUnit, kAudioUnitProperty_MaximumFramesPerSlice,
                                  kAudioUnitScope_Global, 0, &framesPerSlice, &dataSize) == noErr
            && dataSize == sizeof (framesPerSlice) && static_cast<int> (framesPerSlice) != actualBufferSize)
        {
            prepareFloatBuffers (static_cast<int> (framesPerSlice));
        }

        AudioUnitAddPropertyListener (audioUnit, kAudioUnitProperty_StreamFormat, handleStreamFormatChangeCallback, this);

        return true;
    }

    // If the routing is set to go through the receiver (i.e. the speaker, but quiet), this re-routes it
    // to make it loud. Needed because by default when using an input + output, the output is kept quiet.
    static void fixAudioRouteIfSetToReceiver()
    {
        auto session = [AVAudioSession sharedInstance];
        auto route = session.currentRoute;

        for (AVAudioSessionPortDescription* port in route.inputs)
        {
            ignoreUnused (port);
            JUCE_IOS_AUDIO_LOG ("AVAudioSession: input: " << [port.description UTF8String]);
        }

        for (AVAudioSessionPortDescription* port in route.outputs)
        {
            JUCE_IOS_AUDIO_LOG ("AVAudioSession: output: " << [port.description UTF8String]);

            if ([port.portName isEqualToString: @"Receiver"])
            {
                JUCE_NSERROR_CHECK ([session overrideOutputAudioPort: AVAudioSessionPortOverrideSpeaker
                                                               error: &error]);
                setAudioSessionActive (true);
            }
        }
    }

    void handleStreamFormatChange()
    {
        AudioStreamBasicDescription desc;
        zerostruct (desc);
        UInt32 dataSize = sizeof (desc);
        AudioUnitGetProperty(audioUnit,
                             kAudioUnitProperty_StreamFormat,
                             kAudioUnitScope_Output,
                             0,
                             &desc,
                             &dataSize);
        if (desc.mSampleRate != getCurrentSampleRate())
        {
            updateSampleRateAndAudioInput();
            const ScopedLock sl (callbackLock);
            if (callback != nullptr)
            {
                callback->audioDeviceStopped();
                callback->audioDeviceAboutToStart (this);
            }
        }
    }

    static void handleStreamFormatChangeCallback (void* device,
                                                  AudioUnit,
                                                  AudioUnitPropertyID,
                                                  AudioUnitScope scope,
                                                  AudioUnitElement element)
    {
        if (scope == kAudioUnitScope_Output && element == 0)
            static_cast<iOSAudioIODevice*> (device)->handleStreamFormatChange();
    }

    JUCE_DECLARE_NON_COPYABLE (iOSAudioIODevice)
};


//==============================================================================
class iOSAudioIODeviceType  : public AudioIODeviceType
{
public:
    iOSAudioIODeviceType()  : AudioIODeviceType (iOSAudioDeviceName) {}

    void scanForDevices() {}
    StringArray getDeviceNames (bool /*wantInputNames*/) const       { return StringArray (iOSAudioDeviceName); }
    int getDefaultDeviceIndex (bool /*forInput*/) const              { return 0; }
    int getIndexOfDevice (AudioIODevice* d, bool /*asInput*/) const  { return d != nullptr ? 0 : -1; }
    bool hasSeparateInputsAndOutputs() const                         { return false; }

    AudioIODevice* createDevice (const String& outputDeviceName, const String& inputDeviceName)
    {
        if (outputDeviceName.isNotEmpty() || inputDeviceName.isNotEmpty())
            return new iOSAudioIODevice (outputDeviceName.isNotEmpty() ? outputDeviceName : inputDeviceName);

        return nullptr;
    }

private:
    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (iOSAudioIODeviceType)
};

//==============================================================================
AudioIODeviceType* AudioIODeviceType::createAudioIODeviceType_iOSAudio()
{
    return new iOSAudioIODeviceType();
}

//==============================================================================
AudioSessionHolder::AudioSessionHolder()    { nativeSession = [[iOSAudioSessionNative alloc] init: this]; }
AudioSessionHolder::~AudioSessionHolder()   { [nativeSession release]; }

void AudioSessionHolder::handleStatusChange (bool enabled, const char* reason) const
{
    for (auto device: activeDevices)
        device->handleStatusChange (enabled, reason);
}

void AudioSessionHolder::handleRouteChange (const char* reason) const
{
    struct RouteChangeMessage : public CallbackMessage
    {
        RouteChangeMessage (Array<iOSAudioIODevice*> devs, const char* r)
          : devices (devs), changeReason (r)
        {
        }

        void messageCallback() override
        {
            for (auto device: devices)
                device->handleRouteChange (changeReason);
        }

        Array<iOSAudioIODevice*> devices;
        const char* changeReason;
    };

    (new RouteChangeMessage (activeDevices, reason))->post();
}

#undef JUCE_NSERROR_CHECK