[FFmpeg-trac] #1339(avfilter:new): Auto insert fps filter as adapter for overlay filter inputs with different framerates

[FFmpeg]

#1339: Auto insert fps filter as adapter for overlay filter inputs with different
framerates
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             Reporter:  annorax      |                     Type:
               Status:  new          |  enhancement
            Component:  avfilter     |                 Priority:  wish
             Keywords:  fps overlay  |                  Version:  git-
  filter                             |  master
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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 Now that the fps filter has been added (you're my heroes for adding it),
 it would be great if an fps filter would be auto-inserted before the
 overlay filter, where framerate conversion is required if the framerates
 of the two input vary (the way a scale filter is often auto-inserted
 wherever it's required).

 To do this, whenever an overlay filter is used in a filter chain, the
 framerate of each of its inputs should be detected (using the same
 function used by ffprobe to populate the avg_frame_rate property), then
 insert an fps filter to upsample the input with the lower framerate to
 match the framerate of the other one.

 Currently I do this manually: run ffprobe on each video file before
 performing an overlay, then insert an fps filter between the lower-fps
 file and the overlay filter. This means 3 procedure calls. It would be
 great if it could all be done in 1.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1339>
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