[FFmpeg-user] Question about mp3 bit rate mode

[桃源老師]

Hello DopeLabs-san, 

Thanks for your reply.

> 2017/01/31 午後8:41、DopeLabs <dopelabs at dubstep.fm>のメール:
> 
> In your earlier console output for both commands...
> 
>>> size=    2344kB time=00:05:00.01 bitrate=  64.0kbits/s speed= 128x 
> 
>>> size=    2344kB time=00:05:00.01 bitrate=  64.0kbits/s speed= 134x    
> 
> What method are you using to 'verify' the length?

I used macOS's FInder, Windows10's explorer, Windows10's groove music, macOS's iTunes, Windows10's sinkusuperlite, mediainfo, and mpg123.  Then macOS's iTunes and mpg123 show correct length.  Also, mediainfo does not show duration for "$ ffmpeg -f lavfi -i sine=d=300 duration_VBR.mp3 command".

> What is the ffprobe output for each of those files?

With $ ffmpeg -f lavfi -i sine=d=300 duration_VBR.mp3 command:

$ ffprobe -i duration_VBR.mp3 
ffprobe version N-83152-gf7e9275 Copyright (c) 2007-2017 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, mp3, from 'duration_VBR.mp3':
  Metadata:
    encoder         : Lavf57.62.100
  Duration: 00:05:00.04, start: 0.025057, bitrate: 64 kb/s
    Stream #0:0: Audio: mp3, 44100 Hz, mono, s16p, 64 kb/s



With $ ffmpeg -f lavfi -i sine=d=300 -write_xing 0 duration.mp3 command:

$ ffprobe -i duration_CBR.mp3 
ffprobe version N-83152-gf7e9275 Copyright (c) 2007-2017 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
[mp3 @ 0x7fa2fc804e00] Estimating duration from bitrate, this may be inaccurate
Input #0, mp3, from 'duration_CBR.mp3':
  Metadata:
    encoder         : Lavf57.62.100
  Duration: 00:05:00.04, start: 0.000000, bitrate: 64 kb/s
    Stream #0:0: Audio: mp3, 44100 Hz, mono, s16p, 64 kb/s



Best Regards,

// Miya aka. TougenRoushi
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