[FFmpeg-trac] #3542(swresample:new): Changing channel layout from downmix to stereo fails

[FFmpeg]

#3542: Changing channel layout from downmix to stereo fails
------------------------------------+--------------------------------------
             Reporter:  cehoyos     |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  important   |                Component:  swresample
              Version:  git-master  |               Resolution:
             Keywords:  regression  |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
------------------------------------+--------------------------------------

Comment (by cehoyos):

 Since I am not so sure if it is valid at all to write "downmix" to a wav
 file, here is a more realistic alternative:
 {{{
 $ ffmpeg -f s16be -ac 2 -channel_layout DL+DR -i /dev/zero -t 1 -acodec
 pcm_s16be out.mov
 }}}
 {{{
 $ ffmpeg -i out.mov -channel_layout stereo -acodec pcm_s16be out2.mov
 ffmpeg version N-62299-g60ef0c6 Copyright (c) 2000-2014 the FFmpeg
 developers
   built on Apr  9 2014 15:01:30 with gcc 4.7 (SUSE Linux)
   configuration: --enable-gpl
   libavutil      52. 75.100 / 52. 75.100
   libavcodec     55. 58.103 / 55. 58.103
   libavformat    55. 36.102 / 55. 36.102
   libavdevice    55. 11.100 / 55. 11.100
   libavfilter     4.  3.100 /  4.  3.100
   libswscale      2.  6.100 /  2.  6.100
   libswresample   0. 18.100 /  0. 18.100
   libpostproc    52.  3.100 / 52.  3.100
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'out.mov':
   Metadata:
     major_brand     : qt
     minor_version   : 512
     compatible_brands: qt
     encoder         : Lavf55.19.104
   Duration: 00:00:01.00, start: 0.000000, bitrate: 1416 kb/s
     Stream #0:0(eng): Audio: pcm_s16be (twos / 0x736F7774), 44100 Hz,
 downmix, s16, 1411 kb/s (default)
     Metadata:
       handler_name    : DataHandler
 [auto-inserted resampler 0 @ 0x2c99160] [SWR @ 0x2c99580] Input channel
 layout 'downmix' is not supported
 [auto-inserted resampler 0 @ 0x2c99160] Failed to configure output pad on
 auto-inserted resampler 0
 Error opening filters!
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/3542#comment:2>
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