audiooutput.cpp Example File

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

  #include "audiooutput.h"

  #define PUSH_MODE_LABEL "Enable push mode"
  #define PULL_MODE_LABEL "Enable pull mode"
  #define SUSPEND_LABEL   "Suspend playback"
  #define RESUME_LABEL    "Resume playback"
  #define VOLUME_LABEL    "Volume:"

  const int DurationSeconds = 1;
  const int ToneSampleRateHz = 600;
  const int DataSampleRateHz = 44100;
  const int BufferSize      = 32768;

  Generator::Generator(const QAudioFormat &format,
                       qint64 durationUs,
                       int sampleRate,
                       QObject *parent)
      :   QIODevice(parent)
      ,   m_pos(0)
  {
      if (format.isValid())
          generateData(format, durationUs, sampleRate);
  }

  Generator::~Generator()
  {

  }

  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 / 100000;

      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) {
          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 && format.sampleType() == QAudioFormat::UnSignedInt) {
                  const quint8 value = static_cast<quint8>((1.0 + x) / 2 * 255);
                  *reinterpret_cast<quint8*>(ptr) = value;
              } else if (format.sampleSize() == 8 && format.sampleType() == QAudioFormat::SignedInt) {
                  const qint8 value = static_cast<qint8>(x * 127);
                  *reinterpret_cast<quint8*>(ptr) = value;
              } else if (format.sampleSize() == 16 && 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.sampleSize() == 16 && 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;
          }
          ++sampleIndex;
      }
  }

  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))
      ,   m_modeButton(0)
      ,   m_suspendResumeButton(0)
      ,   m_deviceBox(0)
      ,   m_device(QAudioDeviceInfo::defaultOutputDevice())
      ,   m_generator(0)
      ,   m_audioOutput(0)
      ,   m_output(0)
      ,   m_pullMode(true)
      ,   m_buffer(BufferSize, 0)
  {
      initializeWindow();
      initializeAudio();
  }

  void AudioTest::initializeWindow()
  {
      QScopedPointer<QWidget> window(new QWidget);
      QScopedPointer<QVBoxLayout> layout(new QVBoxLayout);

      m_deviceBox = new QComboBox(this);
      const QAudioDeviceInfo &defaultDeviceInfo = QAudioDeviceInfo::defaultOutputDevice();
      m_deviceBox->addItem(defaultDeviceInfo.deviceName(), qVariantFromValue(defaultDeviceInfo));
      foreach (const QAudioDeviceInfo &deviceInfo, QAudioDeviceInfo::availableDevices(QAudio::AudioOutput)) {
          if (deviceInfo != defaultDeviceInfo)
              m_deviceBox->addItem(deviceInfo.deviceName(), qVariantFromValue(deviceInfo));
      }
      connect(m_deviceBox,SIGNAL(activated(int)),SLOT(deviceChanged(int)));
      layout->addWidget(m_deviceBox);

      m_modeButton = new QPushButton(this);
      m_modeButton->setText(tr(PUSH_MODE_LABEL));
      connect(m_modeButton, SIGNAL(clicked()), SLOT(toggleMode()));
      layout->addWidget(m_modeButton);

      m_suspendResumeButton = new QPushButton(this);
      m_suspendResumeButton->setText(tr(SUSPEND_LABEL));
      connect(m_suspendResumeButton, SIGNAL(clicked()), SLOT(toggleSuspendResume()));
      layout->addWidget(m_suspendResumeButton);

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

      window->setLayout(layout.data());
      layout.take(); // ownership transferred

      setCentralWidget(window.data());
      QWidget *const windowPtr = window.take(); // ownership transferred
      windowPtr->show();
  }

  void AudioTest::initializeAudio()
  {
      connect(m_pushTimer, SIGNAL(timeout()), SLOT(pushTimerExpired()));

      m_format.setSampleRate(DataSampleRateHz);
      m_format.setChannelCount(1);
      m_format.setSampleSize(16);
      m_format.setCodec("audio/pcm");
      m_format.setByteOrder(QAudioFormat::LittleEndian);
      m_format.setSampleType(QAudioFormat::SignedInt);

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

      if (m_generator)
          delete m_generator;
      m_generator = new Generator(m_format, DurationSeconds*1000000, ToneSampleRateHz, this);

      createAudioOutput();
  }

  void AudioTest::createAudioOutput()
  {
      delete m_audioOutput;
      m_audioOutput = 0;
      m_audioOutput = new QAudioOutput(m_device, m_format, this);
      m_generator->start();
      m_audioOutput->start(m_generator);
      m_volumeSlider->setValue(int(m_audioOutput->volume()*100.0f));
  }

  AudioTest::~AudioTest()
  {

  }

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

  void AudioTest::volumeChanged(int value)
  {
      if (m_audioOutput)
          m_audioOutput->setVolume(qreal(value/100.0f));
  }

  void AudioTest::pushTimerExpired()
  {
      if (m_audioOutput && m_audioOutput->state() != QAudio::StoppedState) {
          int chunks = m_audioOutput->bytesFree()/m_audioOutput->periodSize();
          while (chunks) {
             const qint64 len = m_generator->read(m_buffer.data(), m_audioOutput->periodSize());
             if (len)
                 m_output->write(m_buffer.data(), len);
             if (len != m_audioOutput->periodSize())
                 break;
             --chunks;
          }
      }
  }

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

      if (m_pullMode) {
          //switch to push mode (periodically push to QAudioOutput using a timer)
          m_modeButton->setText(tr(PULL_MODE_LABEL));
          m_output = m_audioOutput->start();
          m_pullMode = false;
          m_pushTimer->start(20);
      } else {
          //switch to pull mode (QAudioOutput pulls from Generator as needed)
          m_modeButton->setText(tr(PUSH_MODE_LABEL));
          m_pullMode = true;
          m_audioOutput->start(m_generator);
      }

      m_suspendResumeButton->setText(tr(SUSPEND_LABEL));
  }

  void AudioTest::toggleSuspendResume()
  {
      if (m_audioOutput->state() == QAudio::SuspendedState) {
          m_audioOutput->resume();
          m_suspendResumeButton->setText(tr(SUSPEND_LABEL));
      } else if (m_audioOutput->state() == QAudio::ActiveState) {
          m_audioOutput->suspend();
          m_suspendResumeButton->setText(tr(RESUME_LABEL));
      } else if (m_audioOutput->state() == QAudio::StoppedState) {
          m_audioOutput->resume();
          m_suspendResumeButton->setText(tr(SUSPEND_LABEL));
      } else if (m_audioOutput->state() == QAudio::IdleState) {
          // no-op
      }
  }