[FFmpeg-trac] #1717(avfilter:open): Concat filter can not join individual images (was: Concat filter can not join more than two video files)

[FFmpeg]

#1717: Concat filter can not join individual images
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             Reporter:  chinshou    |                    Owner:
                 Type:  defect      |                   Status:  open
             Priority:  minor       |                Component:  avfilter
              Version:  git-master  |               Resolution:
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  1
Analyzed by developer:  1           |
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Changes (by Cigaes):

 * status:  new => open
 * reproduced:  0 => 1
 * priority:  normal => minor
 * version:  unspecified => git-master
 * analyzed:  0 => 1


Comment:

 This is a timestamp problem: concat uses the mean inter-frame interval as
 the duration of the last frame to separate the segments. If a segment is
 made of a single video frame and no audio, then there is no inter-frame
 interval, and the next segment starts at the same time. This will then
 cause frame dropping depending on the vsync algorithm.

 The filter works correctly (AFAIK) if all the segments have more than one
 frame or have audio.

 Temporary workaround: use setpts to shift the time of each segment after a
 single image, or add dummy audio and discard it.

 The problem can be properly fixed when a duration field will be added to
 filtered frames; this is work in progress.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1717#comment:1>
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