[FFmpeg-trac] #3699(avfilter:new): Ability to use expressions using Drawtext to offset frame number without returning double

[FFmpeg]

#3699: Ability to use expressions using Drawtext to offset frame number without
returning double
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             Reporter:  synth     |                     Type:  enhancement
               Status:  new       |                 Priority:  wish
            Component:  avfilter  |                  Version:  git-master
             Keywords:  drawtext  |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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 We have a need for displaying exact frame numbers on generated media from
 ffmpeg. I work in VFX so our input frame sequences can start at any
 arbitrary number for reasons of preroll visualization, not rendering 3d
 elements in the handles of a shot or for frame ranges that start at 1001.
 Currently the only way I've seen for offsetting the drawtext is to do:

 text='%{expr\:n+OFFSET}'

 where OFFSET is the number used for -start_frame. Unfortunately this won't
 work for us because the return value from expr is a double like
 1001.000000 and it doesn't seem there's a way to convert that to int or
 convert it to a value like %04d.

 For us, adding this feature would be incredibly valuable since we rely on
 seeing frame numbers when reviewing media so that we can make notes on
 frames that have errors which is then relayed back to the artist.

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Ticket URL: <https://trac.ffmpeg.org/ticket/3699>
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