QT document reading notes audio example analysis

This example is very interesting , Today I analyzed , Take notes here , Convenient for next reference .

This example shows how to draw dynamic data （ Data input by microphone ）

The interface is as follows ：

The key documents are as follows ：

The official explanation here is gone , I'll add later .

First, we need to learn two classes , Namely ：QAudioInput and QAudioFormat

You can check my blog for details -Qt Document reading notes -QAudioInput&QAudioFormat Analysis and examples .

First, in the main.cpp Key code in ：

const QAudioDeviceInfo inputDevice = QAudioDeviceInfo::defaultInputDevice();
if (inputDevice.isNull()) {
    QMessageBox::warning(nullptr, "audio",
                         "There is no audio input device available.");
    return -1;
}

Here you can check whether the microphone is set in the current system , without , Just quit .

stay Widget.cpp Configuration of the QAudioFormat Related properties , as follows ：

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

 

Parameters	describe
Sample Rate	Audio per second Hertz
Number of channels	Mono or Bi channel
Sample size	Data press 8 Bitstore or 16 Bitstore
Sample type	The type of storage is int still unsigned int still float
Byte order	Save as big end or small end

Finally, let's talk about the most interesting class XYSeriesIODevice. Corresponding

xyseriesiodevice.h：

#ifndef XYSERIESIODEVICE_H
#define XYSERIESIODEVICE_H

#include <QtCore/QIODevice>
#include <QtCore/QPointF>
#include <QtCore/QVector>
#include <QtCharts/QChartGlobal>

QT_CHARTS_BEGIN_NAMESPACE
class QXYSeries;
QT_CHARTS_END_NAMESPACE

QT_CHARTS_USE_NAMESPACE

class XYSeriesIODevice : public QIODevice
{
    Q_OBJECT
public:
    explicit XYSeriesIODevice(QXYSeries *series, QObject *parent = nullptr);

    static const int sampleCount = 2000;

protected:
    qint64 readData(char *data, qint64 maxSize) override;
    qint64 writeData(const char *data, qint64 maxSize) override;

private:
    QXYSeries *m_series;
    QVector<QPointF> m_buffer;
};

#endif // XYSERIESIODEVICE_H

xyseriesiodevice.cpp：

#include "xyseriesiodevice.h"

#include <QtCharts/QXYSeries>
#include <QDebug>

XYSeriesIODevice::XYSeriesIODevice(QXYSeries *series, QObject *parent) :
    QIODevice(parent),
    m_series(series)
{
}

qint64 XYSeriesIODevice::readData(char *data, qint64 maxSize)
{
    Q_UNUSED(data)
    Q_UNUSED(maxSize)
    return -1;
}

qint64 XYSeriesIODevice::writeData(const char *data, qint64 maxSize)
{
    static const int resolution = 4;
    if (m_buffer.isEmpty()) {
        m_buffer.reserve(sampleCount);
        for (int i = 0; i < sampleCount; ++i)
            m_buffer.append(QPointF(i, 0));
    }

    int start = 0;
    const int availableSamples = int(maxSize) / resolution;

    if (availableSamples < sampleCount) {
        start = sampleCount - availableSamples;
        for (int s = 0; s < start; ++s)
            m_buffer[s].setY(m_buffer.at(s + availableSamples).y());
    }

    for (int s = start; s < sampleCount; ++s, data += resolution)
        m_buffer[s].setY(qreal(uchar(*data) - 128) / qreal(128));

    m_series->replace(m_buffer);
    return (sampleCount - start) * resolution;
}

  The key code here is this ：

qint64 XYSeriesIODevice::writeData(const char *data, qint64 maxSize)
{
    static const int resolution = 4;
    if (m_buffer.isEmpty()) {
        m_buffer.reserve(sampleCount);
        for (int i = 0; i < sampleCount; ++i)
            m_buffer.append(QPointF(i, 0));
    }

    int start = 0;
    const int availableSamples = int(maxSize) / resolution;

    if (availableSamples < sampleCount) {
        start = sampleCount - availableSamples;
        for (int s = 0; s < start; ++s)
            m_buffer[s].setY(m_buffer.at(s + availableSamples).y());
    }

    for (int s = start; s < sampleCount; ++s, data += resolution)
        m_buffer[s].setY(qreal(uchar(*data) - 128) / qreal(128));

    m_series->replace(m_buffer);
    return (sampleCount - start) * resolution;
}

The whole curve x The shaft length is ：

static const int sampleCount = 2000;

y Shaft length ：

axisY->setRange(-1, 1);

The audio size is ：

formatAudio.setSampleType(QAudioFormat::UnSignedInt);

This function data Every time I pass 320 One byte, come here , Switch to UnsignedInt Namely 80 individual UnsignedInt.

The following paragraph is right x The axis data is initialized ：

if (m_buffer.isEmpty()) {
    m_buffer.reserve(sampleCount);
    for (int i = 0; i < sampleCount; ++i)
        m_buffer.append(QPointF(i, 0));
}

The following is the data network x The axis moves to the left 1920 A coordinate ：

if (availableSamples < sampleCount) {
    start = sampleCount - availableSamples;
    for (int s = 0; s < start; ++s)
        m_buffer[s].setY(m_buffer.at(s + availableSamples).y());
}

Put the audio just collected to the end 80 In the coordinates （1920~2000）

for (int s = start; s < sampleCount; ++s, data += resolution)
    m_buffer[s].setY(qreal(uchar(*data) - 128) / qreal(128));

here -128 It's to make y Axis has negative number , Divide 128 Because .

axisY->setRange(-1, 1);

Y Axis coordinates are -1, To 1 Between .