[FFmpeg-user] Decimate question

Mark Filipak (ffmpeg) markfilipak at bog.us
Wed Dec 30 19:41:37 EET 2020

On 12/30/2020 03:35 AM, Paul B Mahol wrote:
> On Wed, Dec 30, 2020 at 6:08 AM Mark Filipak (ffmpeg) <markfilipak at bog.us>
> wrote:
>> Decimate will drop a repeated frame in each sequence of 5 (=default)
>> frames. I assume the dropped
>> frame can be any 1 of the 5. Is there a way to discover which of the 5
>> frames it dropped?
> -v debug

May I make a feature request? Could it be added as ... is it called side data?

I haven't used side data yet so I'm not quite sure what it is and how it's used.

The frame # would need to be readable by follow-on logic inside expressions.

This is for processing videos that have previously been telecined, a frame dropped, and a frame 
repeated, in various sequences. The sequence of the video destruction is not important. What's 
important is the phase of the decimation within the modulo-5 in the video that remains. In 4 of the 
5 cases (phases), it's actually possible to almost completely recover the original video (prior to 
the wrecking). 4 out of 5 cases involve the loss of just 1 field in 10. The 5th case involves the 
total loss of a whole frame and is not recoverable (but since that case would have an amazing amount 
of judder, it's unlikely to be found in the wild). However, I have found other cases of this video 
species in the wild.

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