[FFmpeg-trac] #4785(avfilter:reopened): Decimate filter doesn't work when used directly with fieldmatch

[FFmpeg]

#4785: Decimate filter doesn't work when used directly with fieldmatch
-------------------------------------+-------------------------------------
             Reporter:  Detergent    |                    Owner:
                 Type:  defect       |                   Status:  reopened
             Priority:  normal       |                Component:  avfilter
              Version:  git-master   |               Resolution:
             Keywords:  fieldmatch   |               Blocked By:
  decimate pullup                    |  Reproduced by developer:  0
             Blocking:               |
Analyzed by developer:  0            |
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Changes (by Detergent):

 * status:  closed => reopened
 * resolution:  invalid =>


Comment:

 Well, it is progressive content that is telecined.

 Look, using the following :


 {{{
 ffmpeg -i sample.ts -vf fieldmatch -vcodec libx264 out.mkv
 }}}

 generates a 29.97 fps output which has one frame duplicate every 5 frames,
 which is exactly what you'd expect from fieldmatching a telecined content.

 So, so far so good, all we need to do is drop those duplicate frames with
 a cycle of 5. That is what the decimate filter should do, but when used
 directly, it seems to drop more frames than is necessary.

 Except when you use it like this, then it works perfectly and generates an
 excellent 23.976 progressive detelecined content :


 {{{
 ffmpeg -i sample.ts -vf fieldmatch -f yuv4mpegpipe - | ffmpeg -i - -vf
 decimate -vcodec libx264 out.mkv
 }}}

 Because somehow, dropping all the metadata and timestamps and feeding raw
 cfr frames to the decimate filter seems to work much better.

 It would mean a lot if you could do the 2 tests by yourself, and see the
 results. I am certain that the sample IS telecined content, otherwise the
 fieldmatch filter wouldn't work in the first place when processing it.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/4785#comment:11>
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