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

[Mark Filipak]

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.