[FFmpeg-user] Decimation with ppsrc=1 malfunctions

[Paul B Mahol]

On Sun, Dec 27, 2020 at 6:45 PM Mark Filipak (ffmpeg) <markfilipak at bog.us>
wrote:

> On 12/27/2020 06:19 AM, Paul B Mahol wrote:
> > On Sun, Dec 27, 2020 at 5:00 AM Mark Filipak (ffmpeg) <
> markfilipak at bog.us>
> > wrote:
> >
> >> Decimation with ppsrc=1 malfunctions.
>
> >> Paul fixed this somewhat, but it's still in trouble.
> >> Since I eliminated threading and decimation as the cause, I suspect that
> >> frames numbers are being
> >> bollixed.
> >>
> >> The report package is here:
> >> https://www.dropbox.com/t/zu4cezneCJIsdmUu
>
> > decimate filter only drops frames, it never fixes combing.
>
> Of course.
>
> > Do you know exact telecine pattern used in your samples?
>
> Look at 'source.mkv frames 1018-1029.png'. I have a scenario that explains
> why a sober engineer
> would be forced to do what was done, but what's the point? Combing is not
> the issue. The issue is
> that the duplicate (modulo 5) frames found in preprocessed.mkv are not
> being removed from source.mkv.
>
> source.mkv & preprocessed.mkv are 172 frames. target.mkv should be 138
> frames. It is 138 frames, but
> they are the wrong frames. Worse, the frames removed are not modulo 5 but
> vary instead. The only
> cause I could imagine was a mixup due to a threading mixup but
> single-threading didn't solve the
> problem.
>


I really wonder what is your real motivation to write so long text
basically saying nothing.
Decimate filter removes duplicated decombed frames from field match
processing.
Using it for anything other is pointless.

For default cycle of 5 it removes single frame from every 5 frames than
have the lowest threshold.

If you wish to drop every fixed X-th frame from every cycle frames of 5 use
shuffleframes or select filter.



>
> Over to you...  :-)
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