Re: [FFmpeg-devel] [PATCH] cbs_av1: Reject thirty-two zero bits in uvlc code

[Michael Niedermayer <michael@niedermayer.cc>]

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On Sun, Oct 22, 2023 at 07:35:52PM +0100, Mark Thompson wrote:
> The spec allows at least thirty-two zero bits followed by a one to mean
> 2^32-1, with no constraint on the number of zeroes.  The libaom
> reference decoder does not match this, instead reading thirty-two zeroes
> but not the following one to mean 2^32-1.  These two interpretations are
> incompatible and other implementations may follow one or the other.
> Therefore reject thirty-two zeroes because the intended behaviour is not
> clear.
> ---
> libaom, dav1d and SVT-AV1 all have the same nonstandard behaviour of stopping at thirty-two zeroes and not reading the one.  gav1 just rejects thirty-two zeroes.

I would suggest to contact the authors of the spec to bring this discrepancy
to their attention, unless this is already known and
unless this sequence is declared invalid by some other part of the spec
(which would make the discrepancy only occur in invalid sequences)

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are best at talking, realize last or never when they are wrong.

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