On 25/10/2023 21:55, Michael Niedermayer wrote:
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)
<https://github.com/AOMediaCodec/av1-spec/pull/343>
Since this only occurs in nonconforming streams, fixing the spec seems like the
better option.
Thanks,
- Mark
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