[FFmpeg-user] propagation of frames in a filter complex

pdr0 pdr0 at shaw.ca
Thu Apr 16 19:20:08 EEST 2020

To overcome a problem, I'm trying to understand the propagation of frames in
a filter complex.


The behavior is as though because frame n+1==1 can take the [A][C] path, it
does take it & that 
leaves nothing left to also take the [B][D][F] path, so blend never outputs.

I've used 'datascope' in various parts of the filter graph in an attempt to
confirm this on my own. 
It's difficult because my test video doesn't display frame #s.

If that indeed is the behavior, then ...

I need a way to duplicate a frame, # n+1%5==1 in this case, so that the
'blend' operates.

This doesn't answer the question in this thread directly;  but was the idea
still to blend deinterlace the combed frame from telecine selectively ?

If the problem is getting the blend to work on the target, another way is to
use -vf pp=lb with your selection sets.

ffmpeg -i 23.976p_framenumber.mp4 -filter_complex
-c:v libx264 -crf 18 -an out_pp_lb.mkv

Here are 2 framenumber labelled versions for testing,
"23.976p_framenumber.mp4" has the original framenumbers, 240 frames.
"telecine5_framenumbers.mp4" is the output of telecine=5 only, then new
framenumbers put on afterwards . (beware this version has 600 frames because
no select was used with interleave)

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