I use Qt5, and opencv play mp4 file, has a good picture, but I want more sound then I need to do something more

    VideoCapture cap1("/storage/emulated/0/Download/QV5.mp4");
    while(true)
    {
    Mat ft;
    if (cap1.read(ft))
    {
    cv::resize(ft,ft, Size(300, 300),INTER_AREA);   // thay đổi kích thước
    QImage img= QImage((const unsigned char*)(ft.data),
                                        ft.cols,ft.rows,
                                        QImage::Format_BGR888);   // hiển thị
     ui->label_2->setPixmap(QPixmap::fromImage(img));  // show lên label
    }
     QCoreApplication :: processEvents ();
    }

Thanks!