[FFmpeg-devel] [RFC]fps filter

[Carl Eugen Hoyos]

Hi!

I finally realized why -vf fps=30000/1001,fieldmatch,decimate does 
not always work / produces ugly output.
The issue is not related to fieldmatch and/or decimate but to the 
fps filter: It (sometimes) drops frames even if the framerate is 
increased. So the question is: Is it a good idea that fps (iiuc) 
never increases frame duration when increasing the frame rate, not 
even if that would avoid frame drops? What is the use-case for the 
current behaviour?
Work-around is to use -vf dejudder,fps... but I wonder why this 
should be necessary in the general case (and if it really works for 
long samples).

A sample with such timestamps is in  
http://samples.ffmpeg.org/ffmpeg-bugs/trac/ticket3968/
The relevant part starts after 85 seconds iirc. Note that later on, 
the frame rate gets reduced to 20fps, so the output file will never 
look completely clean (at least as long as Michael doesn't commit 
his new fps filter).

ffmpeg -i input -r does not show this behaviour afaict, it does not 
drop frames if it can be avoided.

Carl Eugen