[FFmpeg-user] Question about mp3 bit rate mode

[桃源老師]

Hello ffmpeg experts...

I have question about mp3 bit rate mode.  

When I run the following command, the resulting duration.mp3 is VBR.  I have confirmed it's bit rate mode with mediainfo, mpg123, and SinkuSuperLite (on Windows).

$ ffmpeg -f lavfi -i sine=d=300 duration.mp3
ffmpeg version N-83152-gf7e9275 Copyright (c) 2000-2017 the FFmpeg developers
  built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
  configuration: --prefix=/Volumes/ffmpeg_compile --pkg-config-flags=--static --disable-ffserver --enable-gpl --enable-version3 --enable-nonfree --enable-libmp3lame --enable-libfdk-aac --enable-libvo-amrwbenc --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvorbis --enable-libspeex --enable-libopus --enable-libgsm --enable-libtwolame --enable-libsoxr --enable-libwavpack --enable-libmodplug --enable-libopenjpeg --enable-libwebp --enable-libtheora --enable-libx264 --enable-libopenh264 --enable-libx265 --enable-libxvid --enable-libvpx --enable-libxavs --enable-libfreetype --enable-fontconfig --enable-libfribidi --enable-libass --enable-libbluray --enable-libvidstab --enable-libschroedinger --enable-libsnappy --enable-libzmq
  libavutil      55. 43.100 / 55. 43.100
  libavcodec     57. 74.100 / 57. 74.100
  libavformat    57. 62.100 / 57. 62.100
  libavdevice    57.  2.100 / 57.  2.100
  libavfilter     6. 69.100 /  6. 69.100
  libswscale      4.  3.101 /  4.  3.101
  libswresample   2.  4.100 /  2.  4.100
  libpostproc    54.  2.100 / 54.  2.100
Input #0, lavfi, from 'sine=d=300':
  Duration: N/A, start: 0.000000, bitrate: 705 kb/s
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
Output #0, mp3, to 'duration.mp3':
  Metadata:
    TSSE            : Lavf57.62.100
    Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, mono, s16p
    Metadata:
      encoder         : Lavc57.74.100 libmp3lame
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> mp3 (libmp3lame))
Press [q] to stop, [?] for help
size=    2344kB time=00:05:00.01 bitrate=  64.0kbits/s speed= 128x    
video:0kB audio:2344kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.009457%

And when I run the following command, the resulting duration.mp3 is CBR.  Confirmed with same program as above.

$ ffmpeg -f lavfi -i sine=d=300 -write_xing 0 duration.mp3
ffmpeg version N-83152-gf7e9275 Copyright (c) 2000-2017 the FFmpeg developers
  built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
  configuration: --prefix=/Volumes/ffmpeg_compile --pkg-config-flags=--static --disable-ffserver --enable-gpl --enable-version3 --enable-nonfree --enable-libmp3lame --enable-libfdk-aac --enable-libvo-amrwbenc --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvorbis --enable-libspeex --enable-libopus --enable-libgsm --enable-libtwolame --enable-libsoxr --enable-libwavpack --enable-libmodplug --enable-libopenjpeg --enable-libwebp --enable-libtheora --enable-libx264 --enable-libopenh264 --enable-libx265 --enable-libxvid --enable-libvpx --enable-libxavs --enable-libfreetype --enable-fontconfig --enable-libfribidi --enable-libass --enable-libbluray --enable-libvidstab --enable-libschroedinger --enable-libsnappy --enable-libzmq
  libavutil      55. 43.100 / 55. 43.100
  libavcodec     57. 74.100 / 57. 74.100
  libavformat    57. 62.100 / 57. 62.100
  libavdevice    57.  2.100 / 57.  2.100
  libavfilter     6. 69.100 /  6. 69.100
  libswscale      4.  3.101 /  4.  3.101
  libswresample   2.  4.100 /  2.  4.100
  libpostproc    54.  2.100 / 54.  2.100
Input #0, lavfi, from 'sine=d=300':
  Duration: N/A, start: 0.000000, bitrate: 705 kb/s
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
File 'duration.mp3' already exists. Overwrite ? [y/N] y
Output #0, mp3, to 'duration.mp3':
  Metadata:
    TSSE            : Lavf57.62.100
    Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, mono, s16p
    Metadata:
      encoder         : Lavc57.74.100 libmp3lame
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> mp3 (libmp3lame))
Press [q] to stop, [?] for help
size=    2344kB time=00:05:00.01 bitrate=  64.0kbits/s speed= 134x    
video:0kB audio:2344kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.001875%


I'd like to know why "-write_xing 0" changes bit rate mode of mp3.


Best Regards,


// Miya aka. TougenRoushi

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 2370 bytes
Desc: not available
URL: <http://ffmpeg.org/pipermail/ffmpeg-user/attachments/20170130/bc54efff/attachment.bin>