So far msdk produced dmabuf fds are non-mappable.
If user wants to download the content of underlined surfaces,
dmabufcapsfeature negotiated pipeline will fail. So if the input surface
is dmabuf and downstream doesn't have support for dmabuf capsfeatures,
we do the vpp (no passthrough) and produce the mappable videomemory
buffers.
https://bugzilla.gnome.org/show_bug.cgi?id=794946
prpose_allocation:
-- always instantiate a pool for for upstream
-- use async_depth + 1 as min buffer count
decide_allocation:
-- always create a new bufferpool for source pad.
Each of the msdk element has to create it's own mfxsurfacepool
which is an msdk contraint. For eg: Each Msdk component (vpp, dec and
enc)
will invoke the external Frame allocator for video-memory usage
So sharing the pool between gst-msdk elements might not be a good idea.
https://bugzilla.gnome.org/show_bug.cgi?id=793705
