[FFmpeg-trac] #9845(undetermined:new): gblur sigma=0 and sigmaV=0

[FFmpeg]

#9845: gblur sigma=0 and sigmaV=0
-------------------------------------+-------------------------------------
             Reporter:  Jozef        |                     Type:  defect
  Chutka                             |
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:  glbur        |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Using latest ffmpeg (2022-07-24-git-39a538f430-full_build-www.gyan.dev),
 having parameter `sigmaV=0` for filter `glubr` is causing video to
 disappear:

 {{{
 ffmpeg -i video.mp4 -vf "gblur=sigmaV=0" -y out.mp4
 }}}

 This is the minimal reproducible command and however it might look
 unreasonable, there are multiple reasons why you end up needing
 `sigmaV=0`:

 1. applying horizontal blur only `sigma=10:sigmaV=0`
 2. "animating" sigmaV via `sendcmd=c='0 [expr] gblur sigmaV 100-N`

 Current workaround is to apply some low value `sigmaV=0.001`.

 Slightly different issue appears when using `sigma=0`, which is causing
 vertical blur being ignored:

 {{{
 ffmpeg -i video.mp4 -vf "gblur=sigma=0:sigmaV=10" -y out.mp4
 }}}

 Workaround is to use `sigma=0.001:sigmaV=10`
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9845>
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