Qt 5.9 | Qt Multimedia | Audio Output Example | audiooutput.cpp Example File

Qt 5.9.4 Reference Documentation

# audiooutput.cpp Example File

multimedia/audiooutput/audiooutput.cpp

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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);

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

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

              m_audioOutput->setVolume(linearVolume);
          }
      }

      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
          }
      }