On Sat, Apr 28, 2018 at 10:44:54AM +0200, Jerome Borsboom wrote: > > This patch is not correct. > > > > this code is not used if AV_CODEC_FLAG_BITEXACT is set, because it is > > not bit exact ... > > > > Also the case where the off by 1 error occurs is a rare corner case, > > Compared to the errors introduced by the IDCT this is not significant > > > > If you want to optimize the bit exact version, feel free to do so. > > It may be faster to use xor -1 before and after avg for this though > > Thank you for the review. VC-1 spec is defined bit exact, including the > inverse transform. This code is used by the VC-1 decoder and as I was under > the impression that the VC-1 decoder ought to be bit exact without any > additional > command line options, I tried to resolve the issue.
yes, thats a bug, this should not be used if the whole decoder is bitexactly defined > > As this code is guarded by AV_CODEC_FLAG_BITEXACT, i agree that the > proposed solution is not appropriate. The underlying question remains though. > Should > the VC-1 decoder fully conform to spec or do we allow small deviations? i think it should fully conform, this needs to be fixed can you fix it so the decoder uses only bitexact functions ? (i guess this should be easy by passing the appropriate flag to the init code, but didnt look if the API passes it as seperate argument of passes a context, with a context it may be cleanest to change the internal API ...) thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB While the State exists there can be no freedom; when there is freedom there will be no State. -- Vladimir Lenin
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