audiooutput.cpp Example File

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 #include <QDebug>
 #include <QVBoxLayout>

 #include <QAudioOutput>
 #include <QAudioDeviceInfo>
 #include <QtCore/qmath.h>
 #include <QtCore/qendian.h>
 #include "audiooutput.h"

 const QString AudioTest::PushModeLabel(tr("Enable push mode"));
 const QString AudioTest::PullModeLabel(tr("Enable pull mode"));
 const QString AudioTest::SuspendLabel(tr("Suspend playback"));
 const QString AudioTest::ResumeLabel(tr("Resume playback"));

 const int DurationSeconds = 1;
 const int ToneFrequencyHz = 600;
 const int DataFrequencyHz = 44100;
 const int BufferSize      = 32768;

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

 Generator::~Generator()
 {

 }

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

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

 void Generator::generateData(const QAudioFormat &format, qint64 durationUs, int frequency)
 {
     const int channelBytes = format.sampleSize() / 8;
     const int sampleBytes = format.channels() * channelBytes;

     qint64 length = (format.frequency() * format.channels() * (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 * frequency * qreal(sampleIndex % format.frequency()) / format.frequency());
         for (int i=0; i<format.channels(); ++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;
     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_pullTimer(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_buffer(BufferSize, 0)
 {
     initializeWindow();
     initializeAudio();
 }

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

     m_deviceBox = new QComboBox(this);
     foreach (const QAudioDeviceInfo &deviceInfo, QAudioDeviceInfo::availableDevices(QAudio::AudioOutput))
         m_deviceBox->addItem(deviceInfo.deviceName(), QVariant::fromValue(deviceInfo));
     connect(m_deviceBox,SIGNAL(activated(int)),SLOT(deviceChanged(int)));
     layout->addWidget(m_deviceBox);

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

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

     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_pullTimer, SIGNAL(timeout()), SLOT(pullTimerExpired()));

     m_pullMode = true;

     m_format.setFrequency(DataFrequencyHz);
     m_format.setChannels(1);
     m_format.setSampleSize(16);
     m_format.setCodec("audio/pcm");
     m_format.setByteOrder(QAudioFormat::LittleEndian);
     m_format.setSampleType(QAudioFormat::SignedInt);

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

     m_generator = new Generator(m_format, DurationSeconds*1000000, ToneFrequencyHz, this);

     createAudioOutput();
 }

 void AudioTest::createAudioOutput()
 {
     delete m_audioOutput;
     m_audioOutput = 0;
     m_audioOutput = new QAudioOutput(m_device, m_format, this);
     connect(m_audioOutput, SIGNAL(notify()), SLOT(notified()));
     connect(m_audioOutput, SIGNAL(stateChanged(QAudio::State)), SLOT(stateChanged(QAudio::State)));
     m_generator->start();
     m_audioOutput->start(m_generator);
 }

 AudioTest::~AudioTest()
 {

 }

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

 void AudioTest::notified()
 {
     qWarning() << "bytesFree = " << m_audioOutput->bytesFree()
                << ", " << "elapsedUSecs = " << m_audioOutput->elapsedUSecs()
                << ", " << "processedUSecs = " << m_audioOutput->processedUSecs();
 }

 void AudioTest::pullTimerExpired()
 {
     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_pullTimer->stop();
     m_audioOutput->stop();

     if (m_pullMode) {
         m_modeButton->setText(PullModeLabel);
         m_output = m_audioOutput->start();
         m_pullMode = false;
         m_pullTimer->start(20);
     } else {
         m_modeButton->setText(PushModeLabel);
         m_pullMode = true;
         m_audioOutput->start(m_generator);
     }

     m_suspendResumeButton->setText(SuspendLabel);
 }

 void AudioTest::toggleSuspendResume()
 {
     if (m_audioOutput->state() == QAudio::SuspendedState) {
         qWarning() << "status: Suspended, resume()";
         m_audioOutput->resume();
         m_suspendResumeButton->setText(SuspendLabel);
     } else if (m_audioOutput->state() == QAudio::ActiveState) {
         qWarning() << "status: Active, suspend()";
         m_audioOutput->suspend();
         m_suspendResumeButton->setText(ResumeLabel);
     } else if (m_audioOutput->state() == QAudio::StoppedState) {
         qWarning() << "status: Stopped, resume()";
         m_audioOutput->resume();
         m_suspendResumeButton->setText(SuspendLabel);
     } else if (m_audioOutput->state() == QAudio::IdleState) {
         qWarning() << "status: IdleState";
     }
 }

 void AudioTest::stateChanged(QAudio::State state)
 {
     qWarning() << "state = " << state;
 }