Do not carry over segmentation flags from previous frames. The spec
says in 7.2.10 that the feature data carry over from previous frames
if not updated, but the flags do not.
Consider what would happen if a flag B is to depend on a flag A, and
B carries over as set from another frame. Further consider that A is
now not set in this particular frame. This leads to the invalid state
in which flag B is set but flag A isn't.
This might cause the bitstream to be rejected by accelerators down
the line.
Fix it.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2203>
Existing VP9 parser implementation doesn't provide information
required by other stateless decoding APIs (i.e., DXVA and NVDEC),
specifically loop filter and segmentation parameters might not exist
current frame. So parser needs to fill the information by using previously
parsed information.
We can update the gstvp9parser implementation so that it can provide
all information required by stateless decoding APIs with a huge API break,
or adding more ugly struct in it.
Instead doing as such, this commit introduce a new VP9 parser implementation.
What is different from existing one?
* All variables will follow the specification as much as possible:
VP9 Bitstream & Decoding Process Specification - v0.6 31st March 2016
* Parser will fill all the required information for decoding frame
to GstVp9FrameHeader struct. In case of old VP9 parser,
user needs to read additional data from parser's member variables.
* GstVp9StatefulParser object struct is completely completely opaque
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2112>
