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

[Mark Filipak]

On 28/05/2025 18.15, Paul B Mahol wrote:
> On Wed, May 28, 2025 at 9:35 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.
>>
> 
> Your futile and toxic attempts are in vain.

Thanks for your opinion, Paul. Your desire to distract from real issues is well known to us.

> Detelecine filter is for fixed patterns, other filters try to guess pattern
> by some heuristic which might be correct only in 99.9% cases.

Yes, for static patterns, which 'fieldmatch' can also do.

> Detelecine filter is just an attempt for inverse of telecine filter. And as
> such its primary objective is testing.

An attempt, you say? It's for testing, you say? Gee, I don't remember reading that in the 
documentation. Wasting the valuable word "detelecine" on a test filter is a shame, wouldn't you say?