[FFmpeg-trac] #4376(avfilter:closed): FFmpeg amerge multi input create an output with a lower volume

FFmpeg trac at avcodec.org
Thu Mar 19 19:55:24 CET 2015

#4376: FFmpeg amerge multi input create an output with a lower volume
             Reporter:  wouha        |                    Owner:
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:  avfilter
              Version:  git-master   |               Resolution:  invalid
             Keywords:               |               Blocked By:  low
  filter_complex amerge volume       |  volume
             Blocking:               |  Reproduced by developer:  1
Analyzed by developer:  1            |
Changes (by Cigaes):

 * priority:  important => normal
 * resolution:   => invalid
 * status:  new => closed
 * component:  ffmpeg => avfilter
 * version:  2.6 => git-master


 More precisely, it is exactly six times lower in terms of linear
 intensity. This is the expected behaviour. A lot of PCM hardware and
 software code samples in a bounded interval, usually equivalent to the
 [-1,1] interval after normalization. The problem is that 0.9+0.9=1.8 does
 not fit to the interval; you have to do an average, not a sum:

 That is exactly what "FL<..." does: it is equivalent to "FL=(...)/N",
 where N is the number of channels you added. You are perfectly free to
 write "FL=c0+c2+..." instead of "FL<...". You will get normal volume but
 possibly clipping.

 I do not remember if FFmpeg has soft-clipping filters.

Ticket URL: <https://trac.ffmpeg.org/ticket/4376#comment:1>
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