tdf#145735 qt avmedia: Implement frame grabber

Add a new `QtFrameGrabber` class that implements
the `css::media::XFrameGrabber` interface and
return an instance of it in
`QtPlayer::createFrameGrabber`.

As there seems to be no direct way to retrieve
the image/frame of a video at a certain point
in time, create a separate `QMediaPlayer` instance
for the `QtFrameGrabber`, set a video sink, connect
to its `&QVideoSink::videoFrameChanged` signal and
start playing the video (and stop it again once the
first frame has been received) in order to retrieve
a corresponding frame.

From that `QVideoFrame`, a `QImage` can be retrieved
that can then be converted to an `XGraphic`.

With this in place, a frame from the actual video
is now displaced in Impress in non-presentation
mode instead of just a generic "video icon" placeholder
when opening a presentation containing a video,
(e.g. attachment 145517 from tdf#120452) when the
qt6 VCL plugin is in use.

Change-Id: I3bba3c0fb62a219ac632ceed03ec17f9078f18d0
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/168255
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

0 files changed, 0 insertions, 0 deletions