Opened 7 years ago

Closed 7 years ago

#6549 closed defect (invalid)

low bitrate mp3 encoding result in vbr instead of cbr

Reported by: mboe78 Owned by:
Priority: normal Component: undetermined
Version: git-master Keywords: libmp3lame
Cc: Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no


Summary of the bug:
Regarding to Bug #431 encoding of low bitrate mp3 using ffmpeg results in VBR and not in CBR. Everything encoded lower than 64kbit is affected. Everything higher 64kbit will result in CBR.

How to reproduce:

ffmpeg -i "$infile" -vn -acodec libmp3lame -ac 1 -b:a 32k recode.mp3 

mediainfo recode.mp3
Complete name                            : recode.mp3
Format                                   : MPEG Audio
File size                                : 114 KiB
Overall bit rate mode                    : Variable
Album                                    : XXXXX
Part/Position                            : 01
Part/Total                               : 01
Track name                               : XXXX
Track name/Position                      : 01
Track name/Total                         : 01
Performer                                : XXXX
Recorded date                            : UTC 2017-07-24 00:00:00.0
Writing library                          : Lavf56.40.101
ISRC                                     : GBUM71605388

Format                                   : MPEG Audio
Format version                           : Version 1
Format profile                           : Layer 3
Bit rate mode                            : Variable
Channel(s)                               : 1 channel
Sampling rate                            : 32.0 kHz
Compression mode                         : Lossy
Stream size                              : 113 KiB (100%)

versions affected:
git-snapshot (2017/07/21)

Change History (2)

comment:1 by mboe78, 7 years ago

Workaround found
Adding "-write_xing 0" solved the problem.

comment:2 by Carl Eugen Hoyos, 7 years ago

Component: ffmpegundetermined
Keywords: CBR mp3 removed
Resolution: invalid
Status: newclosed
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