[FFmpeg-trac] #9862(avfilter:new): Can't render subtitles on a transparent video

[FFmpeg]

#9862: Can't render subtitles on a transparent video
-----------------------------------+---------------------------------------
             Reporter:  fduck      |                     Type:  defect
               Status:  new        |                 Priority:  normal
            Component:  avfilter   |                  Version:  unspecified
             Keywords:  subtitles  |               Blocked By:
             Blocking:             |  Reproduced by developer:  0
Analyzed by developer:  0          |
-----------------------------------+---------------------------------------
 Rendering subtitles on a transparent video track (with the alpha option
 set to 1) results in subtitles that don't disappear when they should.
 Later subtitles are drawn right over earlier.
 {{{
 ffmpeg -y\
  -ss 0 -t 15 -i 'video.mov'\
  -filter_complex "
 nullsrc=size=1080x1080 [subtitles];
 [subtitles] subtitles=subtitles.srt:alpha=1 [subtitles];
 [0][subtitles] overlay=x=0:y=0:shortest=1 [out]
 "\
  -map [out] \
  '../test.mp4'
 }}}

 ffmpeg version 5.1
 built with Apple clang version 13.1.6 (clang-1316.0.21.2.5)
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9862>
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