class VideoPreviewProvider : public QQuickImageProvider
{
public:
    VideoPreviewProvider() : QQuickImageProvider(QQuickImageProvider::Image) {}
    QImage requestImage(const QString &imageId, QSize *size, const QSize &requestedSize) override
    {
        QImage preview;
        QEventLoop loop;

        QVideoSink sink;
        QObject::connect(&sink, &QVideoSink::videoFrameChanged, [&] (const QVideoFrame& frame) {
            if (!frame.isValid()) {
                qDebug() << "invalid frame!";
                return;
            }

            preview = frame.toImage();
            loop.quit();
        });

        QMediaPlayer player;
        player.setVideoOutput(&sink);
        player.setSource(QUrl::fromLocalFile(imageId));
        player.play();

        loop.exec();
        return preview;
    }
};