QMediaPlayer 实现频谱

QMediaPlayer是Qt提供的一个多媒体播放器类，可以播放音频和视频文件。要实现频谱，需要使用QAudioProbe类来监听音频输出并获取音频数据，然后使用QAudioSpectrumAnalyzer类来分析音频数据并计算频谱。

具体实现步骤如下：

1. 创建QMediaPlayer对象并设置音频文件路径：

QMediaPlayer *player = new QMediaPlayer;
player->setMedia(QUrl::fromLocalFile("audio.mp3"));

2. 创建QAudioProbe对象并连接到QMediaPlayer的音频输出：

QAudioProbe *probe = new QAudioProbe;
probe->setSource(player);
connect(probe, &QAudioProbe::audioBufferProbed, this, &MyWidget::processBuffer);

3. 实现processBuffer槽函数，用于处理音频数据：

void MyWidget::processBuffer(const QAudioBuffer &buffer)
{
    if (buffer.format().channelCount() != 1) {
        qDebug() << "Only support mono audio";
        return;
    }
    const quint32 numSamples = buffer.frameCount();
    const quint32 sampleRate = buffer.format().sampleRate();
    const quint32 qbytesPerSample = buffer.format().bytesPerFrame();
    const char *data = static_cast<const char *>(buffer.constData());
    QVector<float> samples(numSamples);
    for (quint32 i = 0; i < numSamples; ++i) {
        const char *sample = data + i * qbytesPerSample;
        int value = 0;
        if (qbytesPerSample == 2) {
            value = *reinterpret_cast<const qint16 *>(sample);
        } else if (qbytesPerSample == 4) {
            value = *reinterpret_cast<const qint32 *>(sample) >> 8;
        }
        samples[i] = value / 32768.0;
    }
    QAudioSpectrumAnalyzer spectrum;
    spectrum.setSampleRate(sampleRate);
    spectrum.setChannel(0);
    spectrum.setWindowFunction(QVector<float>(numSamples, 1.0));
    spectrum.setInputData(samples.constData(), numSamples);
    QVector<float> levels = spectrum.calculateLevels();
    // 处理频谱数据
}

4. 在处理频谱数据的代码中，可以使用QPainter绘制出频谱图：

void MyWidget::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.fillRect(rect(), Qt::black);
    painter.setBrush(Qt::red);
    painter.setPen(Qt::NoPen);
    const int numBars = 50;
    const int barWidth = width() / numBars;
    const int heightScale = height() / 100;
    for (int i = 0; i < numBars; ++i) {
        const int level = levels[i * levels.size() / numBars];
        painter.drawRect(i * barWidth, height() - level * heightScale, barWidth, level * heightScale);
    }
}

完整代码示例：

#include <QtWidgets>
#include <QtMultimedia>

class MyWidget : public QWidget
{
    Q_OBJECT
public:
    MyWidget(QWidget *parent = nullptr) : QWidget(parent)
    {
        QMediaPlayer *player = new QMediaPlayer;
        player->setMedia(QUrl::fromLocalFile("audio.mp3"));

        QAudioProbe *probe = new QAudioProbe;
        probe->setSource(player);
        connect(probe, &QAudioProbe::audioBufferProbed, this, &MyWidget::processBuffer);

        QVBoxLayout *layout = new QVBoxLayout(this);
        layout->addWidget(new QLabel("Press Play to start playing audio"));
        QPushButton *playButton = new QPushButton("Play");
        layout->addWidget(playButton);
        connect(playButton, &QPushButton::clicked, player, &QMediaPlayer::play);

        setFixedSize(400, 400);
    }
protected:
    void paintEvent(QPaintEvent *event) override
    {
        QPainter painter(this);
        painter.fillRect(rect(), Qt::black);
        painter.setBrush(Qt::red);
        painter.setPen(Qt::NoPen);
        const int numBars = 50;
        const int barWidth = width() / numBars;
        const int heightScale = height() / 100;
        for (int i = 0; i < numBars; ++i) {
            const int level = levels[i * levels.size() / numBars];
            painter.drawRect(i * barWidth, height() - level * heightScale, barWidth, level * heightScale);
        }
    }
private slots:
    void processBuffer(const QAudioBuffer &buffer)
    {
        if (buffer.format().channelCount() != 1) {
            qDebug() << "Only support mono audio";
            return;
        }
        const quint32 numSamples = buffer.frameCount();
        const quint32 sampleRate = buffer.format().sampleRate();
        const quint32 qbytesPerSample = buffer.format().bytesPerFrame();
        const char *data = static_cast<const char *>(buffer.constData());
        QVector<float> samples(numSamples);
        for (quint32 i = 0; i < numSamples; ++i) {
            const char *sample = data + i * qbytesPerSample;
            int value = 0;
            if (qbytesPerSample == 2) {
                value = *reinterpret_cast<const qint16 *>(sample);
            } else if (qbytesPerSample == 4) {
                value = *reinterpret_cast<const qint32 *>(sample) >> 8;
            }
            samples[i] = value / 32768.0;
        }
        QAudioSpectrumAnalyzer spectrum;
        spectrum.setSampleRate(sampleRate);
        spectrum.setChannel(0);
        spectrum.setWindowFunction(QVector<float>(numSamples, 1.0));
        spectrum.setInputData(samples.constData(), numSamples);
        levels = spectrum.calculateLevels();
        update();
    }
private:
    QVector<float> levels;
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MyWidget widget;
    widget.show();
    return app.exec();
}

#include "main.moc"