If the driver supports it (iHD, so far) and the parameter -d is set,
the direction of the video will be changed randomly.
In the code you can select, at compilation time, if the direction
change is done by element's property or by pipeline events.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2074>
This a GTK+ example will share, through GstContext, a custom X11
VADisplay to a pipeline using vah264dec and appsink.
When the frames are processed for rendering, the VASurfaceID is
fetched from the buffer and it is rendered using vaPutSurface in a X11
widget.
