[FFmpeg-trac] #6997(ffmpeg:new): Last image of the sequence is not shown in the generated video in case it is monochrome and goes after colored image

[FFmpeg]

#6997: Last image of the sequence is not shown in the generated video in case it
is monochrome and goes after colored image
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             Reporter:               |                     Type:  defect
  andriy_lobashchuk                  |                 Priority:  critical
               Status:  new          |                  Version:  3.4
            Component:  ffmpeg       |               Blocked By:
             Keywords:  concat,      |  Reproduced by developer:  0
  fps, demuxer                       |
             Blocking:               |
Analyzed by developer:  0            |
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 Summary of the bug:
 I'm generating the video using concat demuxer with a sequence of images.
 Video has a fade out in the end and each image has a duration specified
 (4.189 sec and 0.03214 for fade in/out transitions).
 In the end of the video, there goes colored image, then monochrome image
 and then the fade out.
 So the main issue is that this colored image is showed not 4.189 but 8.378
 seconds and the monochrome image is not shown at all. The colored image is
 shown instead of the monochrome right till the ending fade out (It can be
 seen in the attached video).

 Is reproducible only with the monochrome image going after colored and fps
 set to 30 (is not reproducible when fps is not set). Two colored is fine,
 two monochrome is fine, monochrome and then colored is fine.

 Hard to say if it is a regression because it worked fine in the ffmpeg
 version 2.8. But after this version, we went straight to the latest 3.4.1

 Attached required files to reproduce the issue (Put images_sequence.txt
 file and images folder into the same directory).
 Full execution report attached.

 How to reproduce:
 {{{
 % ffmpeg -f concat -i images_sequence.txt -vf fps=30 -vcodec h264 -pix_fmt
 yuv420p -preset slower -crf 24 missing_last_image.mp4
 ffmpeg version - 3.4.1
 built on Debain Jessy x64
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/6997>
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