[FFmpeg-trac] #3192(undetermined:new): Dropped Frames With Overlay Filter

[FFmpeg]

#3192: Dropped Frames With Overlay Filter
-------------------------------------+-------------------------------------
             Reporter:  ian_m        |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  git-master   |  undetermined
             Keywords:  x11grab      |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by jnvsor):

 I can confirm it occurs when both streams are passed through
 filter_complex, even if they are null filters that shouldn't effect
 performance at all.

 Low fps:
 {{{
 ffmpeg -f x11grab -framerate 30 -s hd1080 -i :0.0 -f v4l2 -framerate 30 -i
 /dev/video0 -filter_complex '[0]null[cap];[1]null[webcam]' -map '[cap]'
 -map '[webcam]' -c:v libx264 -pix_fmt yuv444p -preset ultrafast -qp 0
 -threads 2 -y out.avi
 }}}

 Remove either of the null filters and it will work at full framerate:
 {{{
 - '[0]null[cap];[1]null[webcam]'
 - -map '[cap]'
 + '[1]null[webcam]'
 + -map 0
 OR
 + '[0]null[cap]'
 + -map 1
 }}}

 Add the v4l2 input first and it will work at full framerate:
 {{{
 - -f x11grab -framerate 30 -s hd1080 -i :0.0 -f v4l2 -framerate 30 -i
 /dev/video0
 + -f v4l2 -framerate 30 -i /dev/video0 -f x11grab -framerate 30 -s hd1080
 -i :0.0
 }}}

 It only occurs if that filter output is actually used, piping one to a
 nullsink also makes it work at full framerate:
 {{{
 - '[0]null[cap];[1]null[webcam]'
 - -map '[cap]'
 + '[0]null[cap];[cap]nullsink;[1]null[webcam]'
 + -map 0
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/3192#comment:11>
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