QVideoFrame::availableMetaData() is always empty

[Amazonasmann]

I have subclassed a QAbstractVideoSurface and set it as output to a QMediaPlayer

   TheMediaPlayer->setVideoOutput(TheSurface);

Inside the QAbstractVideoSurface::present(QVideoFrame) function I require some information about the current frame being displayed. For this I would like to use QVideoFrame::availableMetaData(), but it is always empty. This meta data contains useful information for a frame like when it should be displayed...is it a I, P or B frame etc.

I tried several files, coming from different sources and there is never meta data available in the frame. Is this a Qt bug? What am I doing wrong?

Sidenote: This is a more narrow question to my older question which it seems no one can answer: https://forum.qt.io/topic/106091/qvideoframe-does-not-deliver-correct-starttime-and-endtime-qmediaplayer-issue/4