Qt Reference Documentation

# audiooutput.cpp Example File

multimedia/audiooutput/audiooutput.cpp

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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(), qVariantFromValue(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;
     }