[FFmpeg-trac] #4175(swresample:new): support phase shift for Dolby Pro Logic II / Dolby matrix downmix

[FFmpeg]

#4175: support phase shift for Dolby Pro Logic II / Dolby matrix downmix
-------------------------------------+-------------------------------------
             Reporter:  ranutso      |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  normal       |                Component:
              Version:  git-master   |  swresample
             Keywords:  dplii        |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by otonvm):

 Please check all the samples provided, including the final post-patch
 result.
 Put them into Audacity or similar and even visually the differences are
 obvious.
 Then listen by swithing from solo to solo while playing eash piece on a
 loop.

 Post-patch the difference with reference and/or qaac matrix are minimal at
 best.

 I actually cannot explain what happens... I tried to fix this before I
 found this patch and could not mostly because I did not know how to
 ricreate that phase shift.

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Ticket URL: <https://trac.ffmpeg.org/ticket/4175#comment:8>
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