QString path = QFileDialog::getOpenFileName(this, tr("选择视频"), ".", tr("Image Files(*.mp4)"));//得到视频路径

    mediaPlayer = new QMediaPlayer();

    videoWidget = new QVideoWidget();

    this->setCentralWidget(videoWidget);
     //给VideoWidget画上黑色的背景，这样会更专业点（默认是灰白色的）
     QPalette* palette = new QPalette();

     palette->setBrush(QPalette::Background, Qt::black);

     videoWidget->setPalette(*palette);

     videoWidget->setAutoFillBackground(true);

     delete palette;
     /* 设置播放视频的比例 enum AspectRatioMode { IgnoreAspectRatio, KeepAspectRatio, KeepAspectRatioByExpanding }; */
     videoWidget->setAspectRatioMode(Qt::IgnoreAspectRatio);//保持比例
     mediaPlayer->setVideoOutput(videoWidget);
     //第一种方法：mediaPlayer直接setMedia()
     mediaPlayer->setMedia(QUrl::fromLocalFile(path));
     mediaPlayer->play();