[FFmpeg-user] Confusion about fieldmatch, decimate and framerate (now with yadif)

Carl Eugen Hoyos cehoyos at ag.or.at
Sun Nov 10 05:52:32 CET 2013

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

> Ok, on my current sample. I checked the length and 
> framecount using ffmpeg, getting: Frames: 169698
> Duration: 1:34:19.29 for a frame rate of 29.97.

I apparently miscalculated, sorry.

> In the encode, I get this quite a bit: 
> "Frame #328307 at 10954.5 is still interlaced" So I think, 
> I should add> in yadif=deint=interlaced as per 
> http://ffmpeg.org/ffmpeg-filters.html#Examples-37 between 
> the fieldmatch and the decimate.

Sounds correct and reasonable to me.

>  ffmpeg -i in.mkv -vf libx264 -crf 17 -preset veryfast 
> -vf "fps=30000/10001,fieldmatch,yadif=deint=interlaced,decimate" 
> out-2.mkv
> However, the resulting file is visually the same.

Did you extract the offending frame as fieldmatch outputs 
it and compared it with the same frame as output by 
fieldmatch,yadif=deint=interlaced ?
Every other test is meaningless.

> So I check with 
> ffprobe -show_frames -select_streams v  out.mkv | grep interlaced_frame=1

This tests something else which is 100% unrelated 
(and which you should really ignore / forget if 
you are interested in inverse telecine, there is 
no real world stream that sets this the way you 
test it.)

> I guess fieldmatch doesn't mark the frames it can't 
> deal with. It just leaves them where they are.

This would be a serious bug, if you can actually reproduce it, 
please upload the five-ten relevant frames.

Carl Eugen

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