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

[Mark Filipak]

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.