[FFmpeg-user] Decimation with ppsrc=1 malfunctions

[Mark Filipak (ffmpeg)]

On 12/27/2020 07:30 AM, Carl Eugen Hoyos wrote:
>> Am 27.12.2020 um 12:19 schrieb Paul B Mahol <onemda at gmail.com>:
>>
>> Do you know exact telecine pattern used in your samples?
> 
> I don’t think the sample is telecined...

It must have been. Now, bear with me.
1, The original video was p24:
[A/a][B/b][C/c][D/d]
2, Later, it was telecined:
[A/a][B/b][B/c][C/d][D/d]
3, Later, a modulo-5 frame was dropped [1]:
[A/a][B/c][C/d][D/d]
4, Later, a modulo-4 frame was repeated:
[A/a][B/c][C/d][D/d][D/d]

[1] Dropping a frame in lieu of detelecine was a mistake. Perhaps the engineer was drunk.

>... or at least whatever was done with it can’t be undone (even the description confirms this)...

Ah! But it can be undone (sort of):
Decimate to:
[A/a][B/c][C/d][D/d]
Then synthesize a frame:
[A/a][B/B][B/c][C/d][D/d]
Then detelecine:
[A/a][B/B][C/c][D/d]

>... so this part of the discussion seems moot.

I agree. It's moot because it doesn't bear on why decimate=ppsrc=1 isn't working correctly.