Only a audio heard when a video is playing on preview screen.

Workaround:
VideoWidget::VideoWidget(QWidget *parent)
: QVideoWidget(parent)

{​​​​​​ setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored); QPalette p = palette(); p.setColor(QPalette::Window, Qt::black); setPalette(p); // setAttribute(Qt::WA_OpaquePaintEvent); }

​​​​​​