[VDPAU] ffmpeg and HEVC: Reference handling

[Philip Langdale]

I'm currently trying to work out what's going on with my reference
handling. The code I have today seems to work perfectly fine for
'normal' files - certainly anything x265 or nvenc is willing to spit
out, but it's not doing the right thing for some of the conformance
samples.

The code I've got seems to be internally consistent - I put all the
short and long term refs into RefPics and I can match every entry in
StCurrBefore/StCurrAfter/LtCurr back to those refs. And yet, I'm
getting very visible glitching in the samples.

Of course, for all I know, the glitching is unrelated to ref handling
and is caused by some other feature being used by the samples. :-/

I'm currently excluding all OUTPUT and 'bumping' entries from DPB from
the RefPics[] array. I assume this is the right thing to do, but maybe
that's a mistake?

As for specific glitches, one that really stands out to me is if I try
and decode RPS_C_ericsson_4.bit, everything seems fine until I get to
frame 23, at which point it suddenly outputs a frame that is
bit-identical to frame 21 and then everything goes south from there. I
don't know what to make of that.

--phil