Drop GstVaapiDecoderUnit buffer field (GstBuffer) since it's totally
useless nowadays as creating sub-buffers doesn't bring any value. It
actually means more memory allocations. We can't do without that in
JPEG and MPEG-4:2 decoders.
Use a GArray to hold decoder units in a frame, instead of a single-linked
list. This makes 'append' calls faster, but not that much. At least, this
makes things clearer.
Allocate decoder unit earlier in the main parse() function and don't
delegate this task to derived classes. The ultimate purpose is to get
rid of dynamic allocation of decoder units.
Introduce GstVaapiDecoderUnit which represents a fragment of the source
stream to be decoded. For instance, a decode-unit will be a NAL unit for
H.264 streams, an EBDU for VC-1 streams, and a video packet for MPEG-2
streams.
This is a libgstvaapi internal object.
