This patch adds a GstMemory as a variable member of the buffer proxy,
because we will need to associate the buffer proxy with the memory
which exposes it. Later, we will know which memory, in the video buffer
pool, is attached to the processed surface.
https://bugzilla.gnome.org/show_bug.cgi?id=755072
The support for buffer exports in VA-API was added in version 0.36. These
interfaces are for interop with EGL, OpenCL, etc.
GStreamer-VAAPI uses it for a dmabuf memory allocator. Though, gstreamer-vaapi
has to support VA-API versions ranging from 0.30.4, which doesn't support it.
This patch guards all the buffer exports handling (and dmabuf allocator) if
the detected VA-API version is below 0.36.
https://bugzilla.gnome.org/show_bug.cgi?id=746405
The VA buffer export APIs work for a particular lifetime starting from
vaAcquireBufferHandle() and ending with vaReleaseBufferHandle(). As such,
it could be much more convenient to support implicit releases by simply
having a refcount reaching zero.
https://bugzilla.gnome.org/show_bug.cgi?id=736721
