vdpausink is as the name implies a sink which takes vide/x-vdpau-output buffers
and outputs it to the screen.
vdpauvideopostprocess is an element which takes video/x-vdpau-video buffers and
outputs video/x-vdpau-output buffers. The element can also do things like
deinterlacing and other postprocessing but this is not implemented yet.
the buffers don't come in output order so fix the decoder to handle this
add new gst_vdp_video_buffer_add_reference method to GstVdpVideoBuffer to be able to keep
buffers alive. Ie. a B_FRAME need to have both the forward reference and the backward
reference alive during it's lifetime.
add mutex to protect for threadsafety issues when we reset the decoder in FLUSH_STOP
