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

[FFmpeg]

#4546: -acodec copy doesn't work with AAC VBR
-------------------------------------+-------------------------------------
             Reporter:  ericzutter   |                     Type:  defect
               Status:  new          |                 Priority:  important
            Component:  ffmpeg       |                  Version:
             Keywords:  AAC VBR      |  unspecified
  copy                               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:

 When using "-acodec copy" to extract AAC VBR codec from video, the
 extracted codec becomes AAC CBR. I use MediaInfo CLI to check if AAC codec
 is CBR or VBR.

 How to reproduce:

 1. test.mp4 contains an AAC VBR audio codec
 2. MediaInfo.exe test.mp4 => says "Audio Bitrate mode=variable"
 3. ffmpeg.exe -i test.mp4 -vn -acodec copy test.m4a
 4. MediaInfo.exe test.m4a => says "Audio Bitrate mode=constant"

 Expected result:

 Normally when using '-acodec copy', the "Bitrate mode" on the output
 should be the same as the input.

 My configuration :

 I am using ffmpeg.exe 64 bits with Windows 7-64 bits

 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

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Ticket URL: <https://trac.ffmpeg.org/ticket/4546>
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