[FFmpeg-trac] #4546(undetermined:reopened): -acodec copy doesn't work with AAC VBR

[FFmpeg]

#4546: -acodec copy doesn't work with AAC VBR
-------------------------------------+-------------------------------------
             Reporter:  ericzutter   |                    Owner:
                 Type:  defect       |                   Status:  reopened
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:  AAC          |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------
Changes (by ericzutter):

 * status:  closed => reopened
 * resolution:  needs_more_info =>


Comment:

 Inputfile test.mp4 has metadata AAC audio bitrate mode=variable.

 Ouputfile test.m4a (created using "-acodec copy") has metadata AAC audio
 bitrate mode=constant.

 So test.m4a contains the following:
 Metadata : audio bitrate mode=constant
 Audio bitstream : audio bitrate mode=variable

 When you play test.m4a with an audio player, will the audio player play
 the audio bitstream as a Constant Bitrate Mode or as a Variable Bitrate
 Mode ?

 Does an audio player use the audio bitrate mode info from the metadata to
 play an audio file ?

 How can I view the correct audio bitrate mode from an audio bitstream when
 the audio bitrate mode info in the metadata is not correct ?


 See here the uncut console output :

 ffmpeg.exe -i test.mp4 -vn -acodec copy test.m4a

 ffmpeg version N-71899-g6ef3426 Copyright (c) 2000-2015 the FFmpeg
 developers
   built with gcc 4.9.2 (GCC)
   configuration: --enable-gpl --enable-version3 --disable-w32threads
 --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r
 --enable-gnutls --enable-iconv --enable-libass --enable-libbluray
 --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype
 --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug
 --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb
 --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-
 libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora
 --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-
 libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack
 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs
 --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
   libavutil      54. 23.101 / 54. 23.101
   libavcodec     56. 37.100 / 56. 37.100
   libavformat    56. 31.102 / 56. 31.102
   libavdevice    56.  4.100 / 56.  4.100
   libavfilter     5. 16.101 /  5. 16.101
   libswscale      3.  1.101 /  3.  1.101
   libswresample   1.  1.100 /  1.  1.100
   libpostproc    53.  3.100 / 53.  3.100
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test.mp4':
   Metadata:
     major_brand     : mp42
     minor_version   : 0
     compatible_brands: isomavc1mp42
     creation_time   : 2009-05-28 15:09:33
   Duration: 00:02:51.47, start: 0.000000, bitrate: 2127 kb/s
     Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz,
 stereo, fltp, 125 kb/s (default)
     Metadata:
       creation_time   : 2009-05-28 15:09:33
       handler_name    : (C) 2007 Google Inc. v08.13.2007.
     Stream #0:1(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
 1280x720 [SAR 1:1 DAR 16:9], 1999 kb/s, 29.97 fps, 29.97 tbr, 30k tbn,
 59.94 tbc (default)
     Metadata:
       creation_time   : 2009-05-28 15:09:33
       handler_name    : (C) 2007 Google Inc. v08.13.2007.
 [ipod @ 0000000002dbcbe0] Codec for stream 0 does not use global headers
 but container format requires global headers
 Output #0, ipod, to 'test.m4a':
   Metadata:
     major_brand     : mp42
     minor_version   : 0
     compatible_brands: isomavc1mp42
     encoder         : Lavf56.31.102
     Stream #0:0(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo,
 125 kb/s (default)
     Metadata:
       creation_time   : 2009-05-28 15:09:33
       handler_name    : (C) 2007 Google Inc. v08.13.2007.
 Stream mapping:
   Stream #0:0 -> #0:0 (copy)
 Press [q] to stop, [?] for help
 size=    2651kB time=00:02:51.45 bitrate= 126.7kbits/s
 video:0kB audio:2621kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 1.128996%

--
Ticket URL: <https://trac.ffmpeg.org/ticket/4546#comment:2>
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