[FFmpeg-trac] #4804(undetermined:new): "Buffer queue overflow, dropping." when splitting input into thumbnail and overlay filters.

[FFmpeg]

#4804: "Buffer queue overflow, dropping." when splitting input into thumbnail and
overlay filters.
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             Reporter:  starfires    |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  important    |                Component:
              Version:  git-master   |  undetermined
             Keywords:  regression   |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by Misaki):

 The root cause might be that the thumbnail filter is somehow marking the
 frames as unavailable to 'pass on' to a later filter (or in this case to
 be output to the encoder), even though the stream has supposedly been
 split. I have encountered a bug like this that I hopefully documented
 somewhere but would have to confirm whether it still exists, where some
 type of action on one output of a split filter was affecting the other
 outputs. Maybe trying to change the range from mpeg to pc/jpeg with a
 scale filter without actually modifying the pixels in any other way
 (probably so a lut filter could use that expanded range).

 As a workaround, someone in this very specific situation could try just
 using separate filtergraphs, with a movie filter to add the png. '-vf
 movie=[..],[in]overlay' before the mp4 output, and '-vf thumbnail' before
 the jpeg output. If this works, it suggests the cause is indeed in how the
 filtergraph and specifically the split filter works, and not because there
 is an actual conflict between the thumbnail graph's memory requirements
 and the limited (~64?) number of frames that the overlay filter will
 buffer.

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Ticket URL: <https://trac.ffmpeg.org/ticket/4804#comment:7>
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