audiooutput.cpp Example File

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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
    }
}