[FFmpeg-trac] #11619(avcodec:new): "libopus" downmix (5.1 -> 2ch) unintended volume clipping (was: OPUS downmix volume clipping)

[FFmpeg]

#11619: "libopus" downmix (5.1 -> 2ch) unintended volume clipping
---------------------------------+-----------------------------------
             Reporter:  Marco    |                    Owner:  (none)
                 Type:  defect   |                   Status:  new
             Priority:  normal   |                Component:  avcodec
              Version:  7.1      |               Resolution:
             Keywords:  libopus  |               Blocked By:
             Blocking:           |  Reproduced by developer:  0
Analyzed by developer:  1        |
---------------------------------+-----------------------------------
Changes (by MasterQuestionable):

 * analyzed:  0 => 1
 * cc: MasterQuestionable (added)
 * component:  undetermined => avcodec
 * summary:  OPUS downmix volume clipping => "libopus" downmix (5.1 -> 2ch)
     unintended volume clipping

Comment:

 ͏    Seems "libopus" handled the downmixing wrong..?
 ͏    Try feeding the already-downmixed version?
 ͏    E.g. `ffmpeg -v debug -hide_banner -nostdin -nostats -i "audio.mka"
 -af "channelmap=DL-FL|DR-FR" -c:a libopus -b:a 128k "audio.opus"`

 ͏    Related:
 ͏    https://ffmpeg.org/ffmpeg.html#Audio-Options
 ͏    https://ffmpeg.org/ffmpeg-filters.html#channelmap
 ͏    https://superuser.com/questions/852400/properly-downmix-5-1-to-
 stereo-using-ffmpeg#1410620

 \\
 ͏    Off-Topic:
 ͏    WebP (lossy VP8) is not WebP Lossless.
 ͏    The latter suits the context far better.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11619#comment:2>
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