[FFmpeg-user] Decimation with ppsrc=1 malfunctions

pdr0 pdr0 at shaw.ca
Sun Dec 27 20:32:46 EET 2020

One issue is scene change is still active. When you crop to a region of
interest, a small change is effectively a larger % change. eg. The delta
between 1020 and 1021 is large when head is going up. If you disable scene
change, you get set intervals, it's no longer adaptive by scene change. 

-filter_complex "[0:0][1:0]decimate='ppsrc=1':scthresh=0"

Drops become regular 1012,1017,1022,1027,1032

Other differences are preprocessed.mkv is a lossy version and encoded
progressively instead of interlaced or mbaff. There are motion vectors that
cross fields that shouldn't, so you get motion when you shouldn't when you
examine individual fields. ie. Fields are "muddied" in preprocessed.mkv . 

Also the chroma encoding is different when you encode progressively. You can
see the colored edges are different on some fields. You can set chroma=0 to
disable, or use a proper prepreprocessed version (Lossless and encoded with

These latter two aren't the explanation in this specific case, but you
should test with original source, or lossless versions

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