[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  |               Keywords:  regression
             Blocked By:              |               Blocking:
Reproduced by developer:  0           |  Analyzed by developer:  0
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 This is closely related to ticket #2859.
 Switching the channel layout from downmix to stereo using swresample fails
 since c56d4dab
 {{{
 $ ffmpeg -f s24le -ac 2 -i /dev/zero -t 1 -channel_layout DL+DR -acodec
 copy out.wav
 }}}
 {{{
 $ ffmpeg -i out.wav -channel_layout stereo out2.wav
 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, wav, from 'out.wav':
   Metadata:
     encoder         : Lavf55.36.102
   Duration: 00:00:01.02, bitrate: 2117 kb/s
     Stream #0:0: Audio: pcm_s24le ([1][0][0][0] / 0x0001), 44100 Hz,
 downmix, s32, 2116 kb/s
 [auto-inserted resampler 0 @ 0x24704c0] [SWR @ 0x24440c0] Input channel
 layout 'downmix' is not supported
 [auto-inserted resampler 0 @ 0x24704c0] Failed to configure output pad on
 auto-inserted resampler 0
 Error opening filters!
 }}}
 Work-around is to force the input channel layout:
 {{{
 $ ffmpeg -channel_layout stereo -i out.wav out2.wav
 }}}
 Generally, this is an issue when extracting a downmix stream from a mov
 file: The resulting wav file will not play in QT sine QT doesn't like the
 wav channel layout "downmix".

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