[FFmpeg-user] Confusion about fieldmatch, decimate and framerate

Carl Eugen Hoyos cehoyos at ag.or.at
Fri Nov 8 04:06:10 CET 2013

Nicholas Robbins <nickrobbins <at> yahoo.com> writes:

> > > Uploaded to upload.ffmpeg.org/incoming as
> > sample-robbins.mkv
> > 
> > The sample claims to be 60fps while it actually is 30fps.
> > Assuming you produced the mkv file from a MPEG original:
> > Is the problem also reproducible with the original mpeg 
> > file?
> So I get the original file using mplayer's dumpstream.

Could you provide that sample?
I am not saying there is much difference, but reporting a 
problem with the original sample is generally slightly 
better (I will open a report).

Some random additional comments:
The decimate filter is "stupid", it will produce a cfr 
output that depends on the fps of the input, the filter 
can only work for cfr input with correct frame rate.
You can get this input by using the fps filter first, 
since your sample is (apparently) really 30fps cfr, the 
fps filter neither drops nor duplicates frames, it only 
adjusts the frame rate.
I originally suggested "fps=30000/1001" and "r 24000/1001" 
but it appears to me the sample is actually 30fps (and 
not 29.9), so better values (if the sample is longer than 
one minute) may be "fps=30" and "r 24".

Carl Eugen

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