[FFmpeg-trac] #2852(avcodec:new): dcadec internal default downmix is not normalised and reduces stereo separation by cross mixing L* and R*.

[FFmpeg]

#2852: dcadec internal default downmix is not normalised and reduces stereo
separation by cross mixing L* and R*.
-------------------------------------+-------------------------------------
             Reporter:  AndyF        |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  avcodec      |                  Version:  git-
             Keywords:  dts dca      |  master
  downmix                            |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug: When a dts 5.1 channel is downmixed to stereo with
 -request_channels the results are faulty: not normalised and the  L* and
 R* channels are cross mixed albeit with reduced dB so some stereo effect
 is still perceivable.

 How to reproduce:
 {{{
 % ffmpeg -request_channels 2 -i 6ch.dts 2ch.wav

 ffmpeg version - git

 built on ... 10/08/13
 }}}

 Though this issue seems to exist for all dts samples I have - I don't have
 many and totally failed to find a "normal" VOB channel check.

 The channel check I used was core extracted from 7.1MA.

 Looking at the code it seems that the default matrix in
 libavcodec/dcadata.h looks
 guilty assuming that dca_default_coeffs refers to dca_downmix_coeffs it
 matches with the cross channel mixing that I can hear.

 This also raises the question of why this matrix is used when I expected
 studio dts material to have downmix meta data.

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2852>
FFmpeg <http://ffmpeg.org>
FFmpeg issue tracker