Drop support for user-defined data since this capability was not used
so far and GstVaapiMiniObject represents the smallest reference counted
object type. Add missing GST_VAAPI_MINI_OBJECT_CLASS() helper macro.
Besides, since GstVaapiMiniObject is a libgstvaapi internal object, it
is also possible to further simplify the layout of the object. i.e. merge
GstVaapiMiniObjectBase into GstVaapiMiniObject.
Add gst_vaapi_picture_new_field() function that clones a picture, while
preserving the parent picture surface. i.e. the surface proxy reference
count is increased and other fields copied as is. Besides, the picture
is reset into a "non-output" mode.
VA drivers may have a faster means to transfer user buffers to GPU
buffers than using memcpy(). In particular, on Intel Gen graphics, we
can use pwrite(). This provides for faster upload of bitstream and can
help higher bitrates.
vaapi_create_buffer() helper function was also updated to allow for
un-mapped buffers and pre-initialized data for buffers.
The new API simplifies a lot reference counting and makes it more
flexible for future additions/changes. The GstVaapiCodecInfo is
also gone. Rather, new helper macros are provided to allocate
picture, slice and quantization matrix parameter buffers.
