[FFmpeg-trac] #9681(avfilter:new): drawbox enhancement

[FFmpeg]

#9681: drawbox enhancement
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             Reporter:  Jozef        |                     Type:
  Chutka                             |  enhancement
               Status:  new          |                 Priority:  normal
            Component:  avfilter     |                  Version:
                                     |  unspecified
             Keywords:  drawbox      |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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 I would like to propose the enhancement for drawbox:
 - add time related constants `n` (frame) and `time` (btw `t` is reserved
 for thickness)
 - add `eval=frame` so drawbox is able to recalculate based on changed `n`,
 `time` or dynamic input size `ih`, `iw`
 - add `enable` option so there is a way to restrict its
 availability/rendering

 With these in place, one could draw in-video progress bars, but I believe
 these extensions are generic enough for solid use in different cases as
 well.

 Currently there is an option to use
 [color+overlay](https://stackoverflow.com/questions/62989964/showing-in-
 video-visual-progress-bar-with-ffmpeg), however imagine drawing border
 progress bar (see attachment) which is 4x2 filters already, and I can
 imagine `drawbox` performs faster then either of `color` or `overlay`
 alone.

 Thanks for all the hard work.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9681>
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