We need different export decorators for the different libs.
For now no actual change though, just rename before the release,
and add prelude headers to define the new decorator to GST_EXPORT.
The subsampling_x, subsampling_y, bit_depth, color_space and color_range
fileds are moved from GstVp9FrameHdr to the global GstVp9Parser structure.
These fields are only present in keyframe or intra-only frame, no need to
duplicate them for inter-frames. This is an ABI change.
https://bugzilla.gnome.org/show_bug.cgi?id=764370
