[FFmpeg-trac] #4894(avformat:new): Problem with -acodec copy and AAC VBR

[FFmpeg]

#4894: Problem with -acodec copy and AAC VBR
-------------------------------------+-------------------------------------
             Reporter:  hgg          |                     Type:  defect
               Status:  new          |                 Priority:  minor
            Component:  avformat     |                  Version:  git-
             Keywords:  AAC          |  master
  variable                           |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 It's an extension of https://trac.ffmpeg.org/ticket/4546
 If you extract the AAC VBR track from a file test.m4a to test.aac, then
 reinsert it into another file test2.m4a, it becomes an AAC CBR track if we
 check the metadata with MediaInfo.

 How to reproduce:
 {{{
 ffmpeg -i test.m4a -vn -acodec copy test.aac

 ffmpeg version N-75563-g235381e Copyright (c) 2000-2015 the FFmpeg
 developers
   built with gcc 4.9.3 (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      55.  2.100 / 55.  2.100
   libavcodec     57.  3.100 / 57.  3.100
   libavformat    57.  2.100 / 57.  2.100
   libavdevice    57.  0.100 / 57.  0.100
   libavfilter     6.  8.100 /  6.  8.100
   libswscale      4.  0.100 /  4.  0.100
   libswresample   2.  0.100 /  2.  0.100
   libpostproc    54.  0.100 / 54.  0.100
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test.m4a':
   Metadata:
     major_brand     : M4A
     minor_version   : 512
     compatible_brands: isomiso2
     encoder         : Lavf57.2.100
     gapless_playback: 0
   Duration: 00:00:05.02, start: 0.000000, bitrate: 270 kb/s
     Stream #0:0(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz,
 stereo, fltp, 268 kb/s (default)
     Metadata:
       handler_name    : SoundHandler
 Output #0, adts, to 'test.aac':
   Metadata:
     major_brand     : M4A
     minor_version   : 512
     compatible_brands: isomiso2
     gapless_playback: 0
     encoder         : Lavf57.2.100
     Stream #0:0(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo,
 268 kb/s (default)
     Metadata:
       handler_name    : SoundHandler
 Stream mapping:
   Stream #0:0 -> #0:0 (copy)
 Press [q] to stop, [?] for help
 size=     166kB time=00:00:05.01 bitrate= 270.6kbits/s
 video:0kB audio:164kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 0.899406%
 }}}
 MediaInfo -> AAC Variable

 {{{
 ffmpeg -i test.aac -vn -acodec copy -bsf:a aac_adtstoasc test2.m4a

 ffmpeg version N-75563-g235381e Copyright (c) 2000-2015 the FFmpeg
 developers
   built with gcc 4.9.3 (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      55.  2.100 / 55.  2.100
   libavcodec     57.  3.100 / 57.  3.100
   libavformat    57.  2.100 / 57.  2.100
   libavdevice    57.  0.100 / 57.  0.100
   libavfilter     6.  8.100 /  6.  8.100
   libswscale      4.  0.100 /  4.  0.100
   libswresample   2.  0.100 /  2.  0.100
   libpostproc    54.  0.100 / 54.  0.100
 [aac @ 0000000004fd86c0] Estimating duration from bitrate, this may be
 inaccurate
 Input #0, aac, from 'test.aac':
   Duration: 00:00:05.14, bitrate: 264 kb/s
     Stream #0:0: Audio: aac (LC), 44100 Hz, stereo, fltp, 264 kb/s
 File 'test2.m4a' already exists. Overwrite ? [y/N] y
 [ipod @ 000000000507cce0] Codec for stream 0 does not use global headers
 but container format requires global headers
 Output #0, ipod, to 'test2.m4a':
   Metadata:
     encoder         : Lavf57.2.100
     Stream #0:0: Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, 264
 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (copy)
 Press [q] to stop, [?] for help
 size=     166kB time=00:00:05.01 bitrate= 270.7kbits/s
 video:0kB audio:164kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 0.952347%
 }}}
 MediaInfo -> AAC Constant

 I think the problem is in the way the metadata are created from the raw
 AAC track to the m4a file.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/4894>
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