AudioIO.h

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/**********************************************************************

  Audacity: A Digital Audio Editor

  AudioIO.h

  Dominic Mazzoni

  Use the PortAudio library to play and record sound

**********************************************************************/

#ifndef __AUDACITY_AUDIO_IO__
#define __AUDACITY_AUDIO_IO__

#include "portaudio.h"
#include "Audacity.h"
#include "Experimental.h"

#include "MemoryX.h"
#include <atomic>
#include <utility>
#include <vector>
#include <wx/atomic.h>
#include <wx/weakref.h>

#ifdef USE_MIDI

// TODO: Put the relative paths into automake.

#ifdef EXPERIMENTAL_MIDI_OUT
#include "../lib-src/portmidi/pm_common/portmidi.h"
#include "../lib-src/portmidi/porttime/porttime.h"
#include <cstring> // Allegro include fails if this header isn't included do to no memcpy
#include "../lib-src/header-substitutes/allegro.h"

class NoteTrack;
using NoteTrackArray = std::vector < std::shared_ptr< NoteTrack > >;
using NoteTrackConstArray = std::vector < std::shared_ptr< const NoteTrack > >;

#endif // EXPERIMENTAL_MIDI_OUT

#endif // USE_MIDI

#if USE_PORTMIXER
#include "../lib-src/portmixer/include/portmixer.h"
#endif

#include <wx/event.h>
#include <wx/string.h>
#include <wx/thread.h>

#include "SampleFormat.h"

class AudioIO;
class RingBuffer;
class Mixer;
class Resample;
class TimeTrack;
class AudioThread;
class MeterPanel;
class SelectedRegion;

class AudacityProject;

class WaveTrack;
using WaveTrackArray = std::vector < std::shared_ptr < WaveTrack > >;
using WaveTrackConstArray = std::vector < std::shared_ptr < const WaveTrack > >;

extern AUDACITY_DLL_API AudioIO *gAudioIO;

void InitAudioIO();
void DeinitAudioIO();
wxString DeviceName(const PaDeviceInfo* info);
wxString HostName(const PaDeviceInfo* info);
bool ValidateDeviceNames();

class AudioIOListener;

// #include <cfloat> if you need this constant
#define BAD_STREAM_TIME (-DBL_MAX)

#define MAX_MIDI_BUFFER_SIZE 5000
#define DEFAULT_SYNTH_LATENCY 5

#define DEFAULT_LATENCY_DURATION 100.0
#define DEFAULT_LATENCY_CORRECTION -130.0

#define AUDIO_PRE_ROLL_KEY (wxT("/AudioIO/PreRoll"))
#define DEFAULT_PRE_ROLL_SECONDS 5.0

#define AUDIO_ROLL_CROSSFADE_KEY (wxT("/AudioIO/Crossfade"))
#define DEFAULT_ROLL_CROSSFADE_MS 10.0

#ifdef EXPERIMENTAL_AUTOMATED_INPUT_LEVEL_ADJUSTMENT
   #define AILA_DEF_TARGET_PEAK 92
   #define AILA_DEF_DELTA_PEAK 2
   #define AILA_DEF_ANALYSIS_TIME 1000
   #define AILA_DEF_NUMBER_ANALYSIS 5
#endif

wxDECLARE_EXPORTED_EVENT(AUDACITY_DLL_API,
                         EVT_AUDIOIO_PLAYBACK, wxCommandEvent);
wxDECLARE_EXPORTED_EVENT(AUDACITY_DLL_API,
                         EVT_AUDIOIO_CAPTURE, wxCommandEvent);
wxDECLARE_EXPORTED_EVENT(AUDACITY_DLL_API,
                         EVT_AUDIOIO_MONITOR, wxCommandEvent);

// PRL:
// If we always run a portaudio output stream (even just to produce silence)
// whenever we play Midi, then we might use just one thread for both.
// I thought this would improve MIDI synch problems on Linux/ALSA, but RBD
// convinced me it was neither a necessary nor sufficient fix.  Perhaps too the
// MIDI thread might block in some error situations but we should then not
// also block the audio thread.
// So leave the separate thread ENABLED.
#define USE_MIDI_THREAD

struct ScrubbingOptions;

using PRCrossfadeData = std::vector< std::vector < float > >;

// To avoid growing the argument list of StartStream, add fields here
struct AudioIOStartStreamOptions
{
   explicit
   AudioIOStartStreamOptions(double rate_)
      : timeTrack(NULL)
      , listener(NULL)
      , rate(rate_)
      , playLooped(false)
      , cutPreviewGapStart(0.0)
      , cutPreviewGapLen(0.0)
      , pStartTime(NULL)
      , preRoll(0.0)
   {}

   TimeTrack *timeTrack;
   AudioIOListener* listener;
   double rate;
   bool playLooped;
   double cutPreviewGapStart;
   double cutPreviewGapLen;
   double * pStartTime;
   double preRoll;

#ifdef EXPERIMENTAL_SCRUBBING_SUPPORT
   // Non-null value indicates that scrubbing will happen
   // (do not specify a time track, looping, or recording, which
   //  are all incompatible with scrubbing):
   ScrubbingOptions *pScrubbingOptions {};
#endif

   // contents may get swapped with empty vector
   PRCrossfadeData      *pCrossfadeData{};
};

struct TransportTracks {
   WaveTrackArray playbackTracks;
   WaveTrackArray captureTracks;
#ifdef EXPERIMENTAL_MIDI_OUT
   NoteTrackConstArray midiTracks;
#endif

   // This is a subset of playbackTracks
   WaveTrackConstArray prerollTracks;
};

// This workaround makes pause and stop work when output is to GarageBand,
// which seems not to implement the notes-off message correctly.
#define AUDIO_IO_GB_MIDI_WORKAROUND

int audacityAudioCallback(
   const void *inputBuffer, void *outputBuffer,
   unsigned long framesPerBuffer,
   const PaStreamCallbackTimeInfo *timeInfo,
   PaStreamCallbackFlags statusFlags, void *userData );

// Communicate data from one writer to one reader.
// This is not a queue: it is not necessary for each write to be read.
// Rather loss of a message is allowed:  writer may overwrite.
// Data must be default-constructible and either copyable or movable.
template<typename Data>
class MessageBuffer {
   struct alignas( 64
      //std::hardware_destructive_interference_size // C++17
   ) UpdateSlot {
      std::atomic<bool> mBusy{ false };
      Data mData;
   } mSlots[2];

   std::atomic<unsigned char> mLastWrittenSlot{ 0 };

public:
   void Initialize();

   // Move data out (if available), or else copy it out
   Data Read();
   
   // Copy data in
   void Write( const Data &data );
   // Move data in
   void Write( Data &&data );
};

template<typename Data>
void MessageBuffer<Data>::Initialize()
{
   for (auto &slot : mSlots)
      // Lock both slots first, maybe spinning a little
      while ( slot.mBusy.exchange( true, std::memory_order_acquire ) )
         {}

   mSlots[0].mData = {};
   mSlots[1].mData = {};
   mLastWrittenSlot.store( 0, std::memory_order_relaxed );

   for (auto &slot : mSlots)
      slot.mBusy.exchange( false, std::memory_order_release );
}

template<typename Data>
Data MessageBuffer<Data>::Read()
{
   // Whichever slot was last written, prefer to read that.
   auto idx = mLastWrittenSlot.load( std::memory_order_relaxed );
   idx = 1 - idx;
   bool wasBusy = false;
   do {
      // This loop is unlikely to execute twice, but it might because the
      // producer thread is writing a slot.
      idx = 1 - idx;
      wasBusy = mSlots[idx].mBusy.exchange( true, std::memory_order_acquire );
   } while ( wasBusy );

   // Copy the slot
   auto result = std::move( mSlots[idx].mData );

   mSlots[idx].mBusy.store( false, std::memory_order_release );

   return result;
}

template<typename Data>
void MessageBuffer<Data>::Write( const Data &data )
{
   // Whichever slot was last written, prefer to write the other.
   auto idx = mLastWrittenSlot.load( std::memory_order_relaxed );
   bool wasBusy = false;
   do {
      // This loop is unlikely to execute twice, but it might because the
      // consumer thread is reading a slot.
      idx = 1 - idx;
      wasBusy = mSlots[idx].mBusy.exchange( true, std::memory_order_acquire );
   } while ( wasBusy );

   mSlots[idx].mData = data;
   mLastWrittenSlot.store( idx, std::memory_order_relaxed );

   mSlots[idx].mBusy.store( false, std::memory_order_release );
}

template<typename Data>
void MessageBuffer<Data>::Write( Data &&data )
{
   // Whichever slot was last written, prefer to write the other.
   auto idx = mLastWrittenSlot.load( std::memory_order_relaxed );
   bool wasBusy = false;
   do {
      // This loop is unlikely to execute twice, but it might because the
      // consumer thread is reading a slot.
      idx = 1 - idx;
      wasBusy = mSlots[idx].mBusy.exchange( true, std::memory_order_acquire );
   } while ( wasBusy );

   mSlots[idx].mData = std::move( data );
   mLastWrittenSlot.store( idx, std::memory_order_relaxed );

   mSlots[idx].mBusy.store( false, std::memory_order_release );
}

class AUDACITY_DLL_API AudioIO final {

 public:
   AudioIO();
   ~AudioIO();

   // This function executes in a thread spawned by the PortAudio library
   int AudioCallback(
      const void *inputBuffer, void *outputBuffer,
      unsigned long framesPerBuffer,
      const PaStreamCallbackTimeInfo *timeInfo,
      const PaStreamCallbackFlags statusFlags, void *userData);

   // Part of the callback
   PaStreamCallbackResult CallbackDoSeek();

   // Part of the callback
   void CallbackCheckCompletion(
      int &callbackReturn, unsigned long len);

   AudioIOListener* GetListener() { return mListener; }
   void SetListener(AudioIOListener* listener);

   void StartMonitoring(double sampleRate);

   int StartStream(const TransportTracks &tracks,
                   double t0, double t1,
                   const AudioIOStartStreamOptions &options);

   void StopStream();
   void SeekStream(double seconds) { mSeek = seconds; }

#ifdef EXPERIMENTAL_SCRUBBING_SUPPORT
   bool IsScrubbing() const { return IsBusy() && mScrubState != 0; }

   void UpdateScrub(double endTimeOrSpeed, const ScrubbingOptions &options);

   void StopScrub();

   double GetLastScrubTime() const;
#endif

   bool IsBusy() const;

   bool IsStreamActive() const;
   bool IsStreamActive(int token) const;

   wxLongLong GetLastPlaybackTime() const { return mLastPlaybackTimeMillis; }
   AudacityProject *GetOwningProject() const { return mOwningProject; }

#ifdef EXPERIMENTAL_MIDI_OUT

   PmTimestamp MidiTime();

   // Note: audio code solves the problem of soloing/muting tracks by scanning
   // all playback tracks on every call to the audio buffer fill routine.
   // We do the same for Midi, but it seems wasteful for at least two
   // threads to be frequently polling to update status. This could be
   // eliminated (also with a reduction in code I think) by updating mHasSolo
   // each time a solo button is activated or deactivated. For now, I'm
   // going to do this polling in the FillMidiBuffer routine to localize
   // changes for midi to the midi code, but I'm declaring the variable
   // here so possibly in the future, Audio code can use it too. -RBD
 private:
   bool  mHasSolo; // is any playback solo button pressed?
 public:
   bool SetHasSolo(bool hasSolo);
   bool GetHasSolo() { return mHasSolo; }
#endif

   bool IsAudioTokenActive(int token) const;

   bool IsMonitoring() const;

   void SetPaused(bool state);
   bool IsPaused() const;

   /* Mixer services are always available.  If no stream is running, these
    * methods use whatever device is specified by the preferences.  If a
    * stream *is* running, naturally they manipulate the mixer associated
    * with that stream.  If no mixer is available, output is emulated and
    * input is stuck at 1.0f (a gain is applied to output samples).
    */
   void SetMixer(int inputSource);
   void SetMixer(int inputSource, float inputVolume,
                 float playbackVolume);
   void GetMixer(int *inputSource, float *inputVolume,
                 float *playbackVolume);
   bool InputMixerWorks();

   bool OutputMixerEmulated();

   wxArrayString GetInputSourceNames();

   void HandleDeviceChange();

   static std::vector<long> GetSupportedPlaybackRates(int DevIndex = -1,
                                                double rate = 0.0);

   static std::vector<long> GetSupportedCaptureRates(int devIndex = -1,
                                               double rate = 0.0);

   static std::vector<long> GetSupportedSampleRates(int playDevice = -1,
                                              int recDevice = -1,
                                       double rate = 0.0);

   static int GetOptimalSupportedSampleRate();

   double GetStreamTime();

   sampleFormat GetCaptureFormat() { return mCaptureFormat; }
   unsigned GetNumPlaybackChannels() const { return mNumPlaybackChannels; }
   unsigned GetNumCaptureChannels() const { return mNumCaptureChannels; }

   // Meaning really capturing, not just pre-rolling
   bool IsCapturing() const;

   static const int StandardRates[];
   static const int NumStandardRates;

   wxString GetDeviceInfo();

#ifdef EXPERIMENTAL_MIDI_OUT

   wxString GetMidiDeviceInfo();
#endif

   static bool ValidateDeviceNames(const wxString &play, const wxString &rec);

   #ifdef EXPERIMENTAL_AUTOMATED_INPUT_LEVEL_ADJUSTMENT
      void AILAInitialize();
      void AILADisable();
      bool AILAIsActive();
      void AILAProcess(double maxPeak);
      void AILASetStartTime();
      double AILAGetLastDecisionTime();
   #endif

   bool IsAvailable(AudacityProject *projecT) const;
   void SetCaptureMeter(AudacityProject *project, MeterPanel *meter);
   void SetPlaybackMeter(AudacityProject *project, MeterPanel *meter);

   double GetBestRate(bool capturing, bool playing, double sampleRate);

private:
   void SetMeters();


   bool StartPortAudioStream(double sampleRate,
                             unsigned int numPlaybackChannels,
                             unsigned int numCaptureChannels,
                             sampleFormat captureFormat);
   void FillBuffers();

#ifdef EXPERIMENTAL_MIDI_OUT
   void PrepareMidiIterator(bool send = true, double offset = 0);
   bool StartPortMidiStream();

   // Compute nondecreasing real time stamps, accounting for pauses, but not the
   // synth latency.
   double UncorrectedMidiEventTime();

   void OutputEvent();
   void FillMidiBuffers();
   void GetNextEvent();
   double AudioTime() { return mPlaybackSchedule.mT0 + mNumFrames / mRate; }
   double PauseTime();
   void AllNotesOff(bool looping = false);
#endif

   size_t GetCommonlyFreePlayback();

   size_t GetCommonlyReadyPlayback();

   size_t GetCommonlyAvailCapture();

   static int getRecordDevIndex(const wxString &devName = wxEmptyString);
#if USE_PORTMIXER
   static int getRecordSourceIndex(PxMixer *portMixer);
#endif

   static int getPlayDevIndex(const wxString &devName = wxEmptyString);

   static const int RatesToTry[];
   static const int NumRatesToTry;

   bool AllocateBuffers(
      const AudioIOStartStreamOptions &options,
      const TransportTracks &tracks, double t0, double t1, double sampleRate,
      bool scrubbing );

   void StartStreamCleanup(bool bOnlyBuffers = false);

#ifdef EXPERIMENTAL_MIDI_OUT
   //   MIDI_PLAYBACK:
   PmStream        *mMidiStream;
   PmError          mLastPmError;

   long             mSynthLatency; // ms

   // These fields are used to synchronize MIDI with audio:

   volatile double  mAudioCallbackClockTime;

   volatile long    mNumFrames;
   volatile long    mNumPauseFrames;
   volatile int     mMidiLoopPasses;
   inline double MidiLoopOffset() {
      return mMidiLoopPasses * (mPlaybackSchedule.mT1 - mPlaybackSchedule.mT0);
   }

   volatile long    mAudioFramesPerBuffer;
   volatile bool    mMidiPaused;
   PmTimestamp mMaxMidiTimestamp;

   double mSystemMinusAudioTime;
   double mAudioOutLatency;

   // Next two are used to adjust the previous two, if
   // PortAudio does not provide the info (using ALSA):

   double mStartTime;
   long mCallbackCount;

   volatile double mSystemMinusAudioTimePlusLatency;

   Alg_seq_ptr      mSeq;
   std::unique_ptr<Alg_iterator> mIterator;
   Alg_event_ptr    mNextEvent;

#ifdef AUDIO_IO_GB_MIDI_WORKAROUND
   std::vector< std::pair< int, int > > mPendingNotesOff;
#endif

   double           mNextEventTime;
   NoteTrack        *mNextEventTrack;
   bool             mMidiOutputComplete{ true };
   bool             mNextIsNoteOn;
   bool             mMidiStreamActive;
   bool             mSendMidiState;
   NoteTrackConstArray mMidiPlaybackTracks;
#endif

#ifdef EXPERIMENTAL_AUTOMATED_INPUT_LEVEL_ADJUSTMENT
   bool           mAILAActive;
   bool           mAILAClipped;
   int            mAILATotalAnalysis;
   int            mAILAAnalysisCounter;
   double         mAILAMax;
   double         mAILAGoalPoint;
   double         mAILAGoalDelta;
   double         mAILAAnalysisTime;
   double         mAILALastStartTime;
   double         mAILAChangeFactor;
   double         mAILATopLevel;
   double         mAILAAnalysisEndTime;
   double         mAILAAbsolutStartTime;
   unsigned short mAILALastChangeType;  //0 - no change, 1 - increase change, 2 - decrease change
#endif

   std::unique_ptr<AudioThread> mThread;
#ifdef EXPERIMENTAL_MIDI_OUT
#ifdef USE_MIDI_THREAD
   std::unique_ptr<AudioThread> mMidiThread;
#endif
#endif
   ArrayOf<std::unique_ptr<Resample>> mResample;
   ArrayOf<std::unique_ptr<RingBuffer>> mCaptureBuffers;
   WaveTrackArray      mCaptureTracks;
   ArrayOf<std::unique_ptr<RingBuffer>> mPlaybackBuffers;
   WaveTrackArray      mPlaybackTracks;

   ArrayOf<std::unique_ptr<Mixer>> mPlaybackMixers;
   volatile int        mStreamToken;
   static int          mNextStreamToken;
   double              mFactor;
   double              mRate;

   double              mSeek;
   double              mPlaybackRingBufferSecs;
   double              mCaptureRingBufferSecs;

   size_t              mPlaybackSamplesToCopy;
   size_t              mPlaybackQueueMinimum;

   double              mMinCaptureSecsToCopy;
   bool                mPaused;
   PaStream           *mPortStreamV19;
   bool                mSoftwarePlaythrough;
   bool                mPauseRec;
   float               mSilenceLevel;
   unsigned int        mNumCaptureChannels;
   unsigned int        mNumPlaybackChannels;
   sampleFormat        mCaptureFormat;
   unsigned long long  mLostSamples{ 0 };
   volatile bool       mAudioThreadShouldCallFillBuffersOnce;
   volatile bool       mAudioThreadFillBuffersLoopRunning;
   volatile bool       mAudioThreadFillBuffersLoopActive;

   wxLongLong          mLastPlaybackTimeMillis;

#ifdef EXPERIMENTAL_MIDI_OUT
   volatile bool       mMidiThreadFillBuffersLoopRunning;
   volatile bool       mMidiThreadFillBuffersLoopActive;
#endif

   volatile double     mLastRecordingOffset;
   PaError             mLastPaError;

public:
   wxString            LastPaErrorString();
private:

   AudacityProject    *mOwningProject;
   wxWeakRef<MeterPanel> mInputMeter{};
   MeterPanel         *mOutputMeter;
   bool                mUpdateMeters;
   volatile bool       mUpdatingMeters;

   #if USE_PORTMIXER
   PxMixer            *mPortMixer;
   float               mPreviousHWPlaythrough;
   #endif /* USE_PORTMIXER */

   bool                mEmulateMixerOutputVol;
   bool                mInputMixerWorks;
   float               mMixerOutputVol;

   AudioIOListener*    mListener;

   friend class AudioThread;
#ifdef EXPERIMENTAL_MIDI_OUT
   friend class MidiThread;
#endif

   friend void InitAudioIO();

   bool mUsingAlsa { false };

   // For cacheing supported sample rates
   static int mCachedPlaybackIndex;
   static std::vector<long> mCachedPlaybackRates;
   static int mCachedCaptureIndex;
   static std::vector<long> mCachedCaptureRates;
   static std::vector<long> mCachedSampleRates;
   static double mCachedBestRateIn;
   static double mCachedBestRateOut;

   // Serialize main thread and PortAudio thread's attempts to pause and change
   // the state used by the third, Audio thread.
   wxMutex mSuspendAudioThread;

#ifdef EXPERIMENTAL_SCRUBBING_SUPPORT
   struct ScrubState;
   std::unique_ptr<ScrubState> mScrubState;

   bool mSilentScrub;
   double mScrubSpeed;
   sampleCount mScrubDuration;
#endif

   // A flag tested and set in one thread, cleared in another.  Perhaps
   // this guarantee of atomicity is more cautious than necessary.
   wxAtomicInt mRecordingException {};
   void SetRecordingException()
      { wxAtomicInc( mRecordingException ); }
   void ClearRecordingException()
      { if (mRecordingException) wxAtomicDec( mRecordingException ); }

   std::vector< std::pair<double, double> > mLostCaptureIntervals;
   bool mDetectDropouts{ true };

public:
   // Pairs of starting time and duration
   const std::vector< std::pair<double, double> > &LostCaptureIntervals()
   { return mLostCaptureIntervals; }

   // Used only for testing purposes in alpha builds
   bool mSimulateRecordingErrors{ false };

   // Whether to check the error code passed to audacityAudioCallback to
   // detect more dropouts
   bool mDetectUpstreamDropouts{ true };

private:
   struct RecordingSchedule {
      double mPreRoll{};
      double mLatencyCorrection{}; // negative value usually
      double mDuration{};
      PRCrossfadeData mCrossfadeData;

      // These are initialized by the main thread, then updated
      // only by the thread calling FillBuffers:
      double mPosition{};
      bool mLatencyCorrected{};

      double TotalCorrection() const { return mLatencyCorrection - mPreRoll; }
      double ToConsume() const;
      double Consumed() const;
      double ToDiscard() const;
   } mRecordingSchedule{};

   struct PlaybackSchedule {
      double              mT0;
      double              mT1;
      std::atomic<double> mTime;

      double              mWarpedTime;

      double              mWarpedLength;

      // mWarpedTime and mWarpedLength are irrelevant when scrubbing,
      // else they are used in updating mTime,
      // and when not scrubbing or playing looped, mTime is also used
      // in the test for termination of playback.

      // with ComputeWarpedLength, it is now possible the calculate the warped length with 100% accuracy
      // (ignoring accumulated rounding errors during playback) which fixes the 'missing sound at the end' bug
      
      const TimeTrack *mTimeTrack;
      
      volatile enum {
         PLAY_STRAIGHT,
         PLAY_LOOPED,
#ifdef EXPERIMENTAL_SCRUBBING_SUPPORT
         PLAY_SCRUB,
         PLAY_AT_SPEED, // a version of PLAY_SCRUB.
#endif
      }                   mPlayMode { PLAY_STRAIGHT };
      double              mCutPreviewGapStart;
      double              mCutPreviewGapLen;

      void Init(
         double t0, double t1,
         const AudioIOStartStreamOptions &options,
         const RecordingSchedule *pRecordingSchedule );

      bool ReversedTime() const
      {
         return mT1 < mT0;
      }

      double GetTrackTime() const
      { return mTime.load(std::memory_order_relaxed); }

      void SetTrackTime( double time )
      { mTime.store(time, std::memory_order_relaxed); }

      double ClampTrackTime( double trackTime ) const;

      double LimitTrackTime() const;

      double NormalizeTrackTime() const;

      void ResetMode() { mPlayMode = PLAY_STRAIGHT; }

      bool PlayingStraight() const { return mPlayMode == PLAY_STRAIGHT; }
      bool Looping() const         { return mPlayMode == PLAY_LOOPED; }
      bool Scrubbing() const       { return mPlayMode == PLAY_SCRUB; }
      bool PlayingAtSpeed() const  { return mPlayMode == PLAY_AT_SPEED; }
      bool Interactive() const     { return Scrubbing() || PlayingAtSpeed(); }

      // Returns true if a loop pass, or the sole pass of straight play,
      // is completed at the current value of mTime
      bool PassIsComplete() const;

      // Returns true if time equals t1 or is on opposite side of t1, to t0
      bool Overruns( double trackTime ) const;

      // Compute the NEW track time for the given one and a real duration,
      // taking into account whether the schedule is for looping
      double AdvancedTrackTime(
         double trackTime, double realElapsed, double speed) const;

      // Use the function above in the callback after consuming samples from the
      // playback ring buffers, during usual straight or looping play
      void TrackTimeUpdate(double realElapsed);

      // Convert a nonnegative real duration to an increment of track time
      // relative to mT0.
      double TrackDuration(double realElapsed) const;

      // Convert time between mT0 and argument to real duration, according to
      // time track if one is given; result is always nonnegative
      double RealDuration(double trackTime1) const;

      // How much real time left?
      double RealTimeRemaining() const;

      // Advance the real time position
      void RealTimeAdvance( double increment );

      // Determine starting duration within the first pass -- sometimes not
      // zero
      void RealTimeInit( double trackTime );
      
      void RealTimeRestart();

   } mPlaybackSchedule;

   // Another circular buffer
   // Holds track time values corresponding to every nth sample in the playback
   // buffers, for some large n
   struct TimeQueue {
      Doubles mData;
      size_t mSize{ 0 };
      double mLastTime {};
      // These need not be updated atomically, because we rely on the atomics
      // in the playback ring buffers to supply the synchronization.  Still,
      // align them to avoid false sharing.
      alignas(64) struct Cursor {
         size_t mIndex {};
         size_t mRemainder {};
      } mHead, mTail;

      void Producer(
         const PlaybackSchedule &schedule, double rate, double scrubSpeed,
         size_t nSamples );
      double Consumer( size_t nSamples, double rate );
   } mTimeQueue;
};

#endif