[FFmpeg-devel] [PATCHv2 1/4] avcodec/svq1: fix interframe mean VLC symbols

Michael Niedermayer michael at niedermayer.cc
Thu Oct 20 22:33:31 EEST 2022

On Thu, Oct 20, 2022 at 12:29:53PM +1100, Peter Ross wrote:
> Fixes ticket #128.
> The SVQ1 interframe mean VLC symbols -128 and 128 are incorrectly swapped
> in our SVQ1 implementation, resulting in visible artifacts for some videos.
> This patch unswaps the order of these two symbols.
> The most noticable example of the artiacts caused by this error can be observed in
> https://trac.ffmpeg.org/attachment/ticket/128/svq1_set.7z '352_288_k_50.mov'.
> The artifacts are not observed when using the reference decoder
> (QuickTime 7.7.9 x86 binary).
> As a result of this patch, the reference data for the fate-svq1 test
> ($SAMPLES/svq1/marymary-shackles.mov) must be modified. For this file, our
> decoder output is now bitwise identical to the reference decoder. I have
> tested patch with various other samples and they are all now bitwise identical.
> The SVQ1 encoder also produces different output because of this change, so
> the the vsynth test reference data has also been updated.

The order of the patches should be different because with this first
the encoder and decoder behavior changes and no detection / id is 
updated or used yet

ideally one should be able to checkout any revission on git master and
not generate files that do not decode correctly. 
And files generated from this will get misdetected as old FFmpeg later
if its first



Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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