QT 快速傅里叶绘制QMediaPlayer频谱

在Qt中，可以通过QMediaPlayer和QAudioProbe来获取音频数据，并使用快速傅里叶变换（FFT）算法将其转换为频谱数据。下面是一个简单的示例代码，用于绘制QMediaPlayer的频谱图：

#include <QApplication>
#include <QMainWindow>
#include <QMediaPlayer>
#include <QAudioProbe>
#include <QAudioBuffer>
#include <QPainter>
#include <QTimer>

class SpectrogramWidget : public QWidget
{
public:
    SpectrogramWidget(QWidget *parent = nullptr)
        : QWidget(parent)
        , m_audioProbe(new QAudioProbe(this))
    {
        connect(m_audioProbe, &QAudioProbe::audioBufferProbed,
                this, &SpectrogramWidget::processBuffer);

        m_audioProbe->setSource(nullptr);

        QTimer *timer = new QTimer(this);
        connect(timer, &QTimer::timeout,
                this, &SpectrogramWidget::update);
        timer->start(50); // 更新频率为 20Hz
    }

protected:
    void paintEvent(QPaintEvent *event) override
    {
        QPainter painter(this);

        // 绘制背景
        painter.fillRect(event->rect(), Qt::black);

        // 绘制频谱
        painter.setPen(Qt::green);
        for (int i = 0; i < m_spectrum.size(); ++i) {
            int x = i * width() / m_spectrum.size();
            int y = height() - m_spectrum[i] * height();
            painter.drawLine(x, height(), x, y);
        }
    }

private:
    void processBuffer(const QAudioBuffer &buffer)
    {
        if (buffer.format().channelCount() != 1)
            return;

        const qint16 *data = buffer.constData<qint16>();
        int sampleCount = buffer.frameCount();

        // 计算FFT
        QVector<double> spectrum(sampleCount);
        for (int i = 0; i < sampleCount; ++i) {
            spectrum[i] = data[i] / 32768.0;
        }
        fft(spectrum);

        // 转换为频谱
        QVector<double> freqs(sampleCount / 2);
        for (int i = 0; i < sampleCount / 2; ++i) {
            double re = spectrum[2 * i];
            double im = spectrum[2 * i + 1];
            freqs[i] = sqrt(re * re + im * im);
        }

        m_spectrum = freqs;
    }

    void fft(QVector<double> &data)
    {
        int n = data.size();
        if (n <= 1)
            return;

        QVector<double> even(n / 2);
        QVector<double> odd(n / 2);

        for (int i = 0; i < n / 2; ++i) {
            even[i] = data[2 * i];
            odd[i] = data[2 * i + 1];
        }

        fft(even);
        fft(odd);

        for (int i = 0; i < n / 2; ++i) {
            double re = even[i];
            double im = odd[i] * exp(-2 * M_PI * i / n * I);
            data[i] = re + im;
            data[i + n / 2] = re - im;
        }
    }

    QAudioProbe *m_audioProbe;
    QVector<double> m_spectrum;
};

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

    QMainWindow window;
    SpectrogramWidget *widget = new SpectrogramWidget(&window);
    window.setCentralWidget(widget);
    window.show();

    QMediaPlayer *player = new QMediaPlayer(&window);
    player->setMedia(QUrl::fromLocalFile("music.mp3"));
    player->setVolume(50);
    player->play();

    widget->m_audioProbe->setSource(player);

    return app.exec();
}

在上面的代码中，SpectrogramWidget继承自QWidget，并使用QAudioProbe来获取音频数据。在paintEvent函数中，使用QPainter绘制背景和频谱图。在processBuffer函数中，实现FFT算法并将其应用于音频数据。在fft函数中，实现递归FFT算法。update函数用于更新频谱图的显示。最后，在main函数中，创建一个QMediaPlayer对象并将其与QAudioProbe和SpectrogramWidget相关联。