[FFmpeg-user] 2 pass CBR or VBR not really fixing the bitrate?

Eric Wilde ewilde at gntrains.com
Sun Jul 30 00:35:39 EEST 2017

At 10:51 PM 7/29/2017 +0200, Moritz Barsnick wrote:
>Have you tried using the identical video encoding settings for pass 1
>and pass 2? I seem to recall that that is important.

Interesting that you say that.  I use "-an" for the first pass and then
"-codec:a libmp3lame -b:a 128k" for the second pass when doing two-pass
recording, and it works fine.  My impression was that audio was
irrelevant for the first pass, since you were only building a set of
compression guide data for the video compressor to use in pass two.

> > Can anyone post an example of a case in which ffmpeg really gets CBR or 
> say 110% VBR?
>I can't, but I can point out that ffmpeg mostly does ABR, not CBR.

The parameters above work for me.  I tried VBR and could never get audio
that was synchronized properly with the video, using LAME.  Since 128k,
CBR gives acceptable sound, to my ear, and good compression, I wasn't
about to lose sleep over it.  There's too many other reasons why the
audio doesn't synchronize with the video.  I didn't need a self-inflicted

The bitrate is pegged at 128 Kbps (according to MediaInfo) with this set
of parameters.


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