QtQuick 麥克風採集生成波形圖（一）

本文主要介紹如何從麥克風進行音頻採集，並使用qml-charts模塊進行顯示波形圖顯示

• 首先關於使用電腦的麥克風設備進行音頻採集到內存，可以參考QtQuick音頻採集
• 繼承抽象類QIODevice，並重寫readData()和writeData()兩個方法，readData是從外部讀取數據，暫且不用管它，我們最主要的是重寫writeData()方法，將數據寫入到qml中的ChartView
• 首先在main.qml傳入要操作的序列

Item {
    visible: true
    width: 640
    height: 480

    ChartView{
        id:chartView
        animationOptions: chartView.NoAnimation
        theme: chartView.ChartThemeBlueIcy
        property bool openGL: true
        property bool openGLSupported: true
        anchors.fill: parent

        Component.onCompleted: {
            dataSource.setSeries(chartView.series(0));//傳入要操作的序列QXYSeries
        }

        Component.onDestruction: {
            dataSource.setSeries(0);//銷燬時傳空，在寫入數據時對QXYSeries做非空判斷
        }

        ValueAxis{
            id:axisY1
            min: -1
            max: 1
        }

        ValueAxis{
            id:axisX
            min: 0
            max: 2000
        }

        LineSeries{
            id: lineSeries
            name: "Audio Sample"
            axisX: axisX
            axisY: axisY1
            useOpenGL: chartView.openGL
        }

    }
}

• 在DataSource從qml設置QXYSeries，這裏需要注意的是在ChartView銷燬時需要將它設置爲null，具體請看ChartView中 Component.onDestruction()信號，若不如此，控件在銷燬時仍在執行update操作，這時會出現崩潰現象。

void DataSource::setSeries(QAbstractSeries *series)
{
    m_series = static_cast<QXYSeries *>(series);
}

• writeData()和readData()都是重載函數，這裏其實是接收到錄音設備的數據，然後我們將錄音數據“寫入”到波形圖上

qint64 DataSource::writeData(const char * data, qint64 maxSize)
{
    if(m_series)
    {
        qint64 range = 2000;
        QVector<QPointF> oldPoints = m_series->pointsVector();
        //qDebug() << oldPoints.size();
        QVector<QPointF> points;
        int resolution = 4;

        if (oldPoints.count() < range) {
            points = m_series->pointsVector();
        } else {
            for (int i = maxSize/resolution; i < oldPoints.count(); i++)
                points.append(QPointF(i - maxSize/resolution, oldPoints.at(i).y()));
        }

        qint64 size = points.count();
        for (int k = 0; k < maxSize/resolution; k++)
            points.append(QPointF(k + size, ((quint8)data[resolution * k] - 128)/128.0));

        m_series->replace(points);
    }

    return maxSize;
}

• 3. 最後在main()函數完成初始化等

int main(int argc, char *argv[])
{

    QApplication app(argc, argv);

    QQuickView viewer;

    QObject::connect(viewer.engine(), &QQmlEngine::quit, &viewer, &QWindow::close);

    viewer.setTitle(QStringLiteral("Audio Sample"));

    QAudioFormat formatAudio;
    formatAudio.setSampleRate(8000);
    formatAudio.setChannelCount(1);
    formatAudio.setSampleSize(8);
    formatAudio.setCodec("audio/pcm");
    formatAudio.setByteOrder(QAudioFormat::LittleEndian);
    formatAudio.setSampleType(QAudioFormat::UnSignedInt);

    QAudioDeviceInfo inputDevices = QAudioDeviceInfo::defaultInputDevice();
    QAudioInput* m_audioInput = new QAudioInput(inputDevices,formatAudio);

    DataSource* dataSource = new DataSource();
    dataSource->open(QIODevice::WriteOnly);

    m_audioInput->start(dataSource);
    viewer.rootContext()->setContextProperty("dataSource", dataSource);

    viewer.setSource(QUrl("qrc:/main.qml"));
    viewer.setResizeMode(QQuickView::SizeRootObjectToView);
    viewer.setColor(QColor("#404040"));
    viewer.show();

    return app.exec();
}

效果圖如下

代碼地址 https://github.com/hehis/AudioSamples