If GstVaapiPicture has flag SKIPPED set, this means gst_vaapi_picture_output()
will not push the underlying surface for rendering. Besides, VC-1 skipped P-frame
has nothing to do with rendering. This only means that the currently decoded
picture is just a copy of its reference picture.
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.