audiooutput.cpp Example File

multimedia/audiooutput/audiooutput.cpp 
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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
     }
 }

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