[FFmpeg-user] Why does the 'detelecine' filter exist?

[Alex Xu]

Just to be clear, in the other thread, I got detelecine to work (with the
wrong params?) but couldn't get fieldmatch+decimate to work. But this may
have been due to my files being particularly exotic.

And there's also another inverse detelecine filter called "pullup".

Also, how do you do: configure 'fieldmatch'+'decimate' can be configured to
match the static functionality of 'detelecine'?

I agree that should be in the documentation.

On Wed, May 28, 2025 at 2:35 PM Mark Filipak <markfilipak.imdb at gmail.com>
wrote:

> On 28/05/2025 17.27, Paul B Mahol wrote:
> > On Wed, May 28, 2025 at 9:19 PM Mark Filipak <markfilipak.imdb at gmail.com
> >
> > wrote:
> >
> >> On 28/05/2025 15.39, Alex Xu wrote:
> >>> I recently used the detelecine command in this thread:
> >>> https://ffmpeg.org/pipermail/ffmpeg-user/2025-May/059249.html
> >>>
> >>> I got strange results with the `fieldmatch+decimate` combo, where
> >> decimate
> >>> wasn't removing the correct frame.
> >>>
> >>> I also got strange results with the `pullup` filter.
> >>>
> >>> This may just be because my sample file was really exotic though.
> >>
> >> Yes, there are 'strange' telecines. I've seen 'NTSC' field sequences in
> >> which authors inserted
> >> varying telecined sequences at varying times (when bad timing became
> >> obvious to them) to maintain
> >> running time and sync with audio, and even 'PAL' that took cinema to 25
> >> fps via varying telecine,
> >> again to maintain running time and audio sync. I gave up trying to make
> >> them 24p in the usual ways
> >> and simply 'bobbed' them at 59.940p and 50p.
> >>
> >> None of those experiences justify keeping the 'detelecine' filter.
> >>
> >> I'm simply using 'detelecine' as a clear-cut example of all the filters
> >> that should be deprecated,
> >> or at least marked "obsolete". That would really help novices avoid
> >> headaches.
> >>
> >>
> > But user above just reported only single usecase where detelecine just
> > works for him.
>
> That's not what Alex wrote. Alex wrote "got strange results with the
> `fieldmatch+decimate` combo" --
> which I proceeded to explain. He didn't claim that 'detelecine' works. In
> addition,
> 'fieldmatch'+'decimate' can be configured to match the static
> functionality of 'detelecine', and
> such static matching to a deprecated filter should be included in the
> documentation, as an aid.
>
> The alternative is to continue emasculating FFmpeg.
>
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