Add a global mutex to exclusive access to shared stream buffers, such
as DMABufs or VASurfaces after a tee:
LIBVA_DRIVER_NAME=iHD \
gst-launch-1.0 v4l2src ! tee name=t t. ! queue ! \
vapostproc skin-tone=9 ! xvimagesink \
t. ! queue ! vapostproc ! xvimagesink
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1529>