audiooutput.cpp Example File

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  #include "audiooutput.h"

  #include <QAudioDeviceInfo>
  #include <QAudioOutput>
  #include <QDebug>
  #include <QVBoxLayout>
  #include <qmath.h>
  #include <qendian.h>

  Generator::Generator(const QAudioFormat &format
      , qint64 durationUs
      , int sampleRate)
  {
      if (format.isValid())
          generateData(format, durationUs, sampleRate);
  }

  void Generator::start()
  {
      open(QIODevice::ReadOnly);
  }

  void Generator::stop()
  {
      m_pos = 0;
      close();
  }

  void Generator::generateData(const QAudioFormat &format, qint64 durationUs, int sampleRate)
  {
      const int channelBytes = format.sampleSize() / 8;
      const int sampleBytes = format.channelCount() * channelBytes;
      qint64 length = (format.sampleRate() * format.channelCount() * (format.sampleSize() / 8))
                          * durationUs / 1000000;
      Q_ASSERT(length % sampleBytes == 0);
      Q_UNUSED(sampleBytes) // suppress warning in release builds

      m_buffer.resize(length);
      unsigned char *ptr = reinterpret_cast<unsigned char *>(m_buffer.data());
      int sampleIndex = 0;

      while (length) {
          // Produces value (-1..1)
          const qreal x = qSin(2 * M_PI * sampleRate * qreal(sampleIndex++ % format.sampleRate()) / format.sampleRate());
          for (int i=0; i<format.channelCount(); ++i) {
              if (format.sampleSize() == 8) {
                  if (format.sampleType() == QAudioFormat::UnSignedInt) {
                      const quint8 value = static_cast<quint8>((1.0 + x) / 2 * 255);
                      *reinterpret_cast<quint8 *>(ptr) = value;
                  } else if (format.sampleType() == QAudioFormat::SignedInt) {
                      const qint8 value = static_cast<qint8>(x * 127);
                      *reinterpret_cast<qint8 *>(ptr) = value;
                  }
              } else if (format.sampleSize() == 16) {
                  if (format.sampleType() == QAudioFormat::UnSignedInt) {
                      quint16 value = static_cast<quint16>((1.0 + x) / 2 * 65535);
                      if (format.byteOrder() == QAudioFormat::LittleEndian)
                          qToLittleEndian<quint16>(value, ptr);
                      else
                          qToBigEndian<quint16>(value, ptr);
                  } else if (format.sampleType() == QAudioFormat::SignedInt) {
                      qint16 value = static_cast<qint16>(x * 32767);
                      if (format.byteOrder() == QAudioFormat::LittleEndian)
                          qToLittleEndian<qint16>(value, ptr);
                      else
                          qToBigEndian<qint16>(value, ptr);
                  }
              }

              ptr += channelBytes;
              length -= channelBytes;
          }
      }
  }

  qint64 Generator::readData(char *data, qint64 len)
  {
      qint64 total = 0;
      if (!m_buffer.isEmpty()) {
          while (len - total > 0) {
              const qint64 chunk = qMin((m_buffer.size() - m_pos), len - total);
              memcpy(data + total, m_buffer.constData() + m_pos, chunk);
              m_pos = (m_pos + chunk) % m_buffer.size();
              total += chunk;
          }
      }
      return total;
  }

  qint64 Generator::writeData(const char *data, qint64 len)
  {
      Q_UNUSED(data);
      Q_UNUSED(len);

      return 0;
  }

  qint64 Generator::bytesAvailable() const
  {
      return m_buffer.size() + QIODevice::bytesAvailable();
  }

  AudioTest::AudioTest()
      : m_pushTimer(new QTimer(this))
  {
      initializeWindow();
      initializeAudio(QAudioDeviceInfo::defaultOutputDevice());
  }

  AudioTest::~AudioTest()
  {
      m_pushTimer->stop();
  }

  void AudioTest::initializeWindow()
  {
      QWidget *window = new QWidget;
      QVBoxLayout *layout = new QVBoxLayout;

      m_deviceBox = new QComboBox(this);
      const QAudioDeviceInfo &defaultDeviceInfo = QAudioDeviceInfo::defaultOutputDevice();
      m_deviceBox->addItem(defaultDeviceInfo.deviceName(), qVariantFromValue(defaultDeviceInfo));
      for (auto &deviceInfo: QAudioDeviceInfo::availableDevices(QAudio::AudioOutput)) {
          if (deviceInfo != defaultDeviceInfo)
              m_deviceBox->addItem(deviceInfo.deviceName(), qVariantFromValue(deviceInfo));
      }
      connect(m_deviceBox, QOverload<int>::of(&QComboBox::activated), this, &AudioTest::deviceChanged);
      layout->addWidget(m_deviceBox);

      m_modeButton = new QPushButton(this);
      connect(m_modeButton, &QPushButton::clicked, this, &AudioTest::toggleMode);
      layout->addWidget(m_modeButton);

      m_suspendResumeButton = new QPushButton(this);
      connect(m_suspendResumeButton, &QPushButton::clicked, this, &AudioTest::toggleSuspendResume);
      layout->addWidget(m_suspendResumeButton);

      QHBoxLayout *volumeBox = new QHBoxLayout;
      m_volumeLabel = new QLabel;
      m_volumeLabel->setText(tr("Volume:"));
      m_volumeSlider = new QSlider(Qt::Horizontal);
      m_volumeSlider->setMinimum(0);
      m_volumeSlider->setMaximum(100);
      m_volumeSlider->setSingleStep(10);
      connect(m_volumeSlider, &QSlider::valueChanged, this, &AudioTest::volumeChanged);
      volumeBox->addWidget(m_volumeLabel);
      volumeBox->addWidget(m_volumeSlider);
      layout->addLayout(volumeBox);

      window->setLayout(layout);

      setCentralWidget(window);
      window->show();
  }

  void AudioTest::initializeAudio(const QAudioDeviceInfo &deviceInfo)
  {
      QAudioFormat format;
      format.setSampleRate(44100);
      format.setChannelCount(1);
      format.setSampleSize(16);
      format.setCodec("audio/pcm");
      format.setByteOrder(QAudioFormat::LittleEndian);
      format.setSampleType(QAudioFormat::SignedInt);

      if (!deviceInfo.isFormatSupported(format)) {
          qWarning() << "Default format not supported - trying to use nearest";
          format = deviceInfo.nearestFormat(format);
      }

      const int durationSeconds = 1;
      const int toneSampleRateHz = 600;
      m_generator.reset(new Generator(format, durationSeconds * 1000000, toneSampleRateHz));
      m_audioOutput.reset(new QAudioOutput(deviceInfo, format));
      m_generator->start();

      qreal initialVolume = QAudio::convertVolume(m_audioOutput->volume(),
                                                  QAudio::LinearVolumeScale,
                                                  QAudio::LogarithmicVolumeScale);
      m_volumeSlider->setValue(qRound(initialVolume * 100));
      toggleMode();
  }

  void AudioTest::deviceChanged(int index)
  {
      m_generator->stop();
      m_audioOutput->stop();
      m_audioOutput->disconnect(this);
      initializeAudio(m_deviceBox->itemData(index).value<QAudioDeviceInfo>());
  }

  void AudioTest::volumeChanged(int value)
  {
      qreal linearVolume = QAudio::convertVolume(value / qreal(100),
                                                 QAudio::LogarithmicVolumeScale,
                                                 QAudio::LinearVolumeScale);

      m_audioOutput->setVolume(linearVolume);
  }

  void AudioTest::toggleMode()
  {
      m_pushTimer->stop();
      m_audioOutput->stop();
      toggleSuspendResume();

      if (m_pullMode) {
          //switch to pull mode (QAudioOutput pulls from Generator as needed)
          m_modeButton->setText(tr("Enable push mode"));
          m_audioOutput->start(m_generator.data());
      } else {
          //switch to push mode (periodically push to QAudioOutput using a timer)
          m_modeButton->setText(tr("Enable pull mode"));
          auto io = m_audioOutput->start();
          m_pushTimer->disconnect();

          connect(m_pushTimer, &QTimer::timeout, [this, io]() {
              if (m_audioOutput->state() == QAudio::StoppedState)
                  return;

              QByteArray buffer(32768, 0);
              int chunks = m_audioOutput->bytesFree() / m_audioOutput->periodSize();
              while (chunks) {
                 const qint64 len = m_generator->read(buffer.data(), m_audioOutput->periodSize());
                 if (len)
                     io->write(buffer.data(), len);
                 if (len != m_audioOutput->periodSize())
                     break;
                 --chunks;
              }
          });

          m_pushTimer->start(20);
      }

      m_pullMode = !m_pullMode;
  }

  void AudioTest::toggleSuspendResume()
  {
      if (m_audioOutput->state() == QAudio::SuspendedState || m_audioOutput->state() == QAudio::StoppedState) {
          m_audioOutput->resume();
          m_suspendResumeButton->setText(tr("Suspend recording"));
      } else if (m_audioOutput->state() == QAudio::ActiveState) {
          m_audioOutput->suspend();
          m_suspendResumeButton->setText(tr("Resume playback"));
      } else if (m_audioOutput->state() == QAudio::IdleState) {
          // no-op
      }
  }