- Qt 5.5
- Qt Multimedia
- Audio Output Example
- audiooutput.cpp Example File
- Qt 5.5.1 Reference Documentation

# audiooutput.cpp Example File

audiooutput/audiooutput.cpp

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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_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_pullMode = true;

        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(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, 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);
        m_volumeSlider->setValue(int(m_audioOutput->volume()*100.0f));
    }

    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>();
        createAudioOutput();
    }

    void AudioTest::volumeChanged(int value)
    {
        if (m_audioOutput)
            m_audioOutput->setVolume(qreal(value/100.0f));
    }

    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
        }
    }