原理

c = 质数数组长度，除不了就c--，都除不了c==0，while(0)退出循环。

mainwindow.h

struct WbiH {
    int width;
    int height;
};

WbiH calcWbiH(int w, int h);

mainwindow.cpp

{
   ......
   int width = player->metaData(SLMD.at(i)).toSize().width();
   int height = player->metaData(SLMD.at(i)).toSize().height();
   WbiH wbih = calcWbiH(width, height);
   //qDebug() << wbih.width << "X" << wbih.height;
   s += SLMD.at(i) + ": " + QString::number(width) + " X " + QString::number(height) + " (" + QString::number(wbih.width) + ":" + QString::number(wbih.height) + ")\n";
   ......
}

WbiH MainWindow::calcWbiH(int w, int h)
{
    QList<int> zs;
    zs << 2 << 3 << 5 << 7 << 11;
    int c = zs.length();
    while (c) {
        c = zs.length();
        for (int i=0; i<zs.length(); i++) {
            if (w % zs.at(i) == 0 && h % zs.at(i) == 0) {
                w = w / zs.at(i);
                h = h / zs.at(i);
            } else {
                c--;
            }
        }
        qDebug() << c;
    }
    return WbiH{w, h};
}