Audio Output Example

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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
    }
}