We did several things to enable the new memory logic in msdkdec:
(1) We always use video memory for decoder in linux path;
(2) We give negotiated pool to alloc_pool stored in GstMsdkContext which
will be used in callback mfxFrameAllocator:Alloc to alloc surfaces as
MediaSDK needs, and this pool is also available for decoder itself;
(3) We modify decide_allocation process, that is we make pool negotiaion
before gst_msdk_init_decoder to ensure the pool is decided and ready for
use in mfxFrameAllocator:Alloc callback; then we will consider the case
when we need to do the gpu to cpu copy.
(4) In gst_msdkdec_finish_task, we modify the way for copy following the
logic in (3).
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3439>
Add a pool creation function name as 2 for later use which will create
va pool for video memory in linux and keep system pool for windows.
This gst_msdkdec_create_buffer_pool2 will replace gst_msdkdec_create_buffer_pool
when all the memory allocation modifications are ready in the commits after.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3439>
Msdkdec should use it own pool when the allocation from downstream query
is not any msdk_allocator (i.e. msdk_video_allocator,
msdk_dmabuf_allocator and msdk_system_allocator). Otherwise, when using
pipeline "msdkh264dec ! vah264enc !" to transcode a not 16-bit-aligned
stream (i.e. 1920x1080), the transcoding will fail due to the size
mismatch issue between decoder pool and encoder pool.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2451>
