A classic case of not enough locking.
One interesting thing with this is the interaction between the
rotation value and caps negotiation. i.e. the width/height of the caps
can be swapped depending on the video-direction property. We can't lock
the entirety of the caps negotiation for obvious reasons so we need to
do something else. This takes the approach of trying to use a single
rotation value throughout the entirety of the negotiation and then
subsequent output frame in a kind of latching sequence.
Fixes: https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/issues/792
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/836>
