[FFmpeg-devel] [PATCH] avcodec/x86/hpeldsp: fix half pel interpolation

[Rostislav Pehlivanov]

On 28 April 2018 at 10:42, Hendrik Leppkes <h.leppkes at gmail.com> wrote:

> On Sat, Apr 28, 2018 at 10:44 AM, Jerome Borsboom
> <jerome.borsboom at carpalis.nl> 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.
> >
> > 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?
>
> If the spec is bitexact, then our decoder should be by default as
> well. Perhaps such things should be flipped around and use bitexact by
> default unless the "fast" flag is specified.
>
> - Hendrik
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I'd say just remove it, it'll bitrot otherwise since no one will use it.