[FFmpeg-trac] #3298(undetermined:new): overlay filter odd stuttering depending on order of input

[FFmpeg]

#3298: overlay filter odd stuttering depending on order of input
-------------------------------------+-------------------------------------
             Reporter:  jnvsor       |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Overlaying v4l2 onto x11grab causes a large drop in framerate for x11grab
 in certain input order
 {{{
 ffmpeg \
 -f x11grab -framerate 30 -s hd1080 -i :0.0 \
 -f v4l2 -framerate 30 -i /dev/video0 \
 -filter_complex '[0][1]overlay=x=300:y=300[cap]' \
 -map '[cap]' \
 -c:v libx264 -pix_fmt yuv444p -preset ultrafast -qp 0 \
 -threads 2 -y out.avi
 # frame=  225 fps= 18 q=-1.0 Lsize=   36782kB time=00:00:12.56
 bitrate=23977.3kbits/s dup=0 drop=74
 }}}

 Switching the input order (And the filter inputs to keep the same output)
 {{{
 ffmpeg \
 -f v4l2 -framerate 30 -i /dev/video0 \
 -f x11grab -framerate 30 -s hd1080 -i :0.0 \
 -filter_complex '[1][0]overlay=x=300:y=300[cap]' \
 -map '[cap]' \
 -c:v libx264 -pix_fmt yuv444p -preset ultrafast -qp 0 \
 -threads 2 -y out.avi
 # frame=  208 fps= 30 q=-1.0 Lsize=   25993kB time=00:00:06.93
 bitrate=30711.3kbits/s
 }}}
 The frame by frame of this video is also far smoother. Where the previous
 video had 4/5 frames duplicated in a row, this never exceeds 1.

 Recording to separate output tracks is still smooth, but the cause isn't a
 bottleneck in the filter. Splitting the x11grab input and overlaying that
 retains a high framerate.

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Ticket URL: <https://trac.ffmpeg.org/ticket/3298>
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