[FFmpeg-trac] #2859(swresample:open): -ac downmix fails.

[FFmpeg]

#2859: -ac downmix fails.
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             Reporter:  Mista_D     |                    Owner:
                 Type:  defect      |                   Status:  open
             Priority:  important   |                Component:  swresample
              Version:  git-master  |               Resolution:
             Keywords:  regression  |               Blocked By:
             Blocking:              |  Reproduced by developer:  1
Analyzed by developer:  0           |
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Comment (by Cigaes):

 I confirm the downmixing is at fault, not the sample. It can be observed
 using the following command:
 {{{./tools/make_chlayout_test FL+FR+FC+LFE+BL+BR+DL+DR -ac 2
 /tmp/2ch.wav}}}
 The resulting file says "front left, front right", but should be saying
 "downmix left, downmix right".

 The commit you are pointing seems to be doing half the work: when
 converting to stereo from a layout that has DL+DR, the matrix should just
 map DL to FL and DR to FR and drop the rest. Instead, it maps FL and FR.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2859#comment:2>
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