Chaining 4 video fade filters does not work

[Claudiu Lazar]

Summary of the bug: When I try to chain 4 video fade filters the overlay isn't shown at all, it works if I removed the last 2 fades.

How to reproduce:

ffmpeg -report -v 9 -loglevel 99 -y \
  -f lavfi -r 30 -i color=c=blue:s=1920x1080:d=10:rate=30,format=rgba \
  -f lavfi -r 30 -i color=c=yellow:s=300x200:d=10:rate=30,format=rgba \
  -filter_complex \
    '[1]format=rgba,
        fade=t=in:st=0:d=2:alpha=1,
        fade=t=out:st=2:d=2:alpha=1,
        fade=t=in:st=4:d=2:alpha=1,
        fade=t=out:st=6:d=2:alpha=1 [ovl];
     [0][ovl]overlay=shortest=1:format=auto[v]' \
  -map '[v]' -c:v libx264 -pix_fmt yuv420p double.mp4

ffmpeg version N-119376-g8ea11dcd84
built on 29-april-2025

[Claudiu Lazar]

Log file from report

[Claudiu Lazar]

output with loglevel 99

[Gyan]

See ​https://stackoverflow.com/q/38166233/ for how the fade filter works, and how to effect multiple fades.