Add the helper function _get_surface_id() which extracts the
VASurfaceID from the passed picture. This function gets the surface of
the next and previous reference picture.
Instead of if-statements, this refactor uses a switch-statement with a
fall-through, for P-type pictures, making the code a bit more readable.
Also it adds quirks for gallium driver, which cannot handle invalid
surfaces as forwarding nor backwarding references, so the function fails.
Also iHD cannot handle them, but to avoid failing, the current picture
is used as self-reference.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1939>
When missing the reference frames, we should not just discard the current
frame. Some streams have group of picture header. It is an optional header
that can be used immediately before a coded I-frame to indicate to the decoder
if the first consecutive B-pictures immediately following the coded I-frame can
be reconstructed properly in the case of a random access.
In that case, the B frames may miss the previous reference and can still be
correctly decoded. We also notice that the second field of the I frame may
be set to P type, and it only ref its first field.
We should not skip all those frames, and even the frame really misses the
reference frame, some manner such as inserting grey picture should be used
to handle these cases.
The driver crashes when it needs to access the reference picture while we set
forward_reference_picture or backward_reference_picture to VA_INVALID_ID. We
now set it to current picture to avoid this. This is just a temp manner.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1929>
