[FFmpeg-trac] #4823(undetermined:open): Conversion from DTS/DTS-MA to AC3 results in 2 channels instead of 6

[FFmpeg]

#4823: Conversion from DTS/DTS-MA to AC3 results in 2 channels instead of 6
-------------------------------------+-------------------------------------
             Reporter:  JohnGalt     |                    Owner:
                 Type:  defect       |                   Status:  open
             Priority:  normal       |                Component:
              Version:  git-master   |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------

Comment (by cehoyos):

 There is definitely a bug, it is just unknown whether the bug is in the
 documentation or the code:
 https://ffmpeg.org/ffmpeg-all.html#Audio-Options mentions the same
 {{{stream_specifier}}} for {{{-ac}}} as https://ffmpeg.org/ffmpeg-all.html
 #Main-options for {{{-codec}}} but the following does not work as
 documented:
 {{{
 $ ffmpeg -i fate-suite/svq3/Vertical400kbit.sorenson3.mov -c:a:0 ac3 -ac:0
 2 out.avi
 ffmpeg version N-78323-gaa75157 Copyright (c) 2000-2016 the FFmpeg
 developers
   built with gcc 4.7 (SUSE Linux)
   configuration: --enable-gpl --enable-libmp3lame
   libavutil      55. 17.100 / 55. 17.100
   libavcodec     57. 24.101 / 57. 24.101
   libavformat    57. 24.101 / 57. 24.101
   libavdevice    57.  0.101 / 57.  0.101
   libavfilter     6. 28.100 /  6. 28.100
   libswscale      4.  0.100 /  4.  0.100
   libswresample   2.  0.101 /  2.  0.101
   libpostproc    54.  0.100 / 54.  0.100
 Guessed Channel Layout for  Input Stream #0.1 : mono
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'fate-
 suite/svq3/Vertical400kbit.sorenson3.mov':
   Metadata:
     creation_time   : 2001-03-20 16:17:18
     title           : Vertical Online SV3 Demo
     title-eng       : Vertical Online SV3 Demo
     artist          : Logan Kelsey
     artist-eng      : Logan Kelsey
     copyright       : © Vertical Online 2001
     copyright-eng   : © Vertical Online 2001
     encoder         : Sorenson Video 3
     encoder-eng     : Sorenson Video 3
   Duration: 00:00:43.58, start: 0.000000, bitrate: 580 kb/s
     Stream #0:0(eng): Video: svq3 (SVQ3 / 0x33515653), yuvj420p(pc),
 320x240, 391 kb/s, 30.02 fps, 30 tbr, 600 tbn, 600 tbc (default)
     Metadata:
       creation_time   : 2001-03-20 16:17:18
       handler_name    : Apple Alias Data Handler
       encoder         : Sorenson Video 3
     Stream #0:1(eng): Audio: adpcm_ima_qt (ima4 / 0x34616D69), 44100 Hz, 1
 channels, s16p, 176 kb/s (default)
     Metadata:
       creation_time   : 2001-03-20 16:17:18
       handler_name    : Apple Alias Data Handler
 [swscaler @ 0x25fc740] deprecated pixel format used, make sure you did set
 range correctly
 enc->bits_per_coded_sample: 0
 blkalign: 3840
 bytespersec: 12000
 Output #0, avi, to 'out.avi':
   Metadata:
     ISFT            : Lavf57.24.101
     INAM            : Vertical Online SV3 Demo
     title-eng       : Vertical Online SV3 Demo
     IART            : Logan Kelsey
     artist-eng      : Logan Kelsey
     ICOP            : © Vertical Online 2001
     copyright-eng   : © Vertical Online 2001
     Stream #0:0(eng): Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 320x240,
 q=2-31, 200 kb/s, 30 fps, 30 tbn, 30 tbc (default)
     Metadata:
       creation_time   : 2001-03-20 16:17:18
       handler_name    : Apple Alias Data Handler
       encoder         : Lavc57.24.101 mpeg4
     Side data:
       unknown side data type 10 (24 bytes)
     Stream #0:1(eng): Audio: ac3 ([0] [0][0] / 0x2000), 44100 Hz, mono,
 fltp, 96 kb/s (default)
     Metadata:
       creation_time   : 2001-03-20 16:17:18
       handler_name    : Apple Alias Data Handler
       encoder         : Lavc57.24.101 ac3
 Stream mapping:
   Stream #0:0 -> #0:0 (svq3 (native) -> mpeg4 (native))
   Stream #0:1 -> #0:1 (adpcm_ima_qt (native) -> ac3 (native))
 Press [q] to stop, [?] for help
 Multiple frames in a packet from stream 1
 frame= 1308 fps=1234 q=2.0 Lsize=    1732kB time=00:00:43.60 bitrate=
 325.4kbits/s speed=41.1x
 video:1151kB audio:511kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 4.234080%
 }}}
 The following - unexpectedly - does produce stereo output:
 {{{
 $ ffmpeg -i fate-suite/svq3/Vertical400kbit.sorenson3.mov -c:a:0 ac3 -ac:1
 2 out.avi
 }}}
 Not a regression afaict.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/4823#comment:11>
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