Qt 5.11 | Qt Multimedia | Audio Output Example | audiooutput.cpp Example File

Qt 5.11.3 Reference Documentation

# audiooutput.cpp Example File

multimedia/audiooutput/audiooutput.cpp

      /****************************************************************************
      **
      ** Copyright (C) 2017 The Qt Company Ltd.
      ** Contact: https://www.qt.io/licensing/
      **
      ** This file is part of the examples of the Qt Toolkit.
      **
      ** $QT_BEGIN_LICENSE:BSD$
      ** Commercial License Usage
      ** Licensees holding valid commercial Qt licenses may use this file in
      ** accordance with the commercial license agreement provided with the
      ** Software or, alternatively, in accordance with the terms contained in
      ** a written agreement between you and The Qt Company. For licensing terms
      ** and conditions see https://www.qt.io/terms-conditions. For further
      ** information use the contact form at https://www.qt.io/contact-us.
      **
      ** BSD License Usage
      ** Alternatively, you may use this file under the terms of the BSD license
      ** as follows:
      **
      ** "Redistribution and use in source and binary forms, with or without
      ** modification, are permitted provided that the following conditions are
      ** met:
      **   * Redistributions of source code must retain the above copyright
      **     notice, this list of conditions and the following disclaimer.
      **   * Redistributions in binary form must reproduce the above copyright
      **     notice, this list of conditions and the following disclaimer in
      **     the documentation and/or other materials provided with the
      **     distribution.
      **   * Neither the name of The Qt Company Ltd nor the names of its
      **     contributors may be used to endorse or promote products derived
      **     from this software without specific prior written permission.
      **
      **
      ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
      ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
      ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
      ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
      ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
      ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
      ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
      ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
      ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
      ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
      ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
      **
      ** $QT_END_LICENSE$
      **
      ****************************************************************************/

      #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
          }
      }