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

Manuel Tiglio tiglio at icloud.com
Sat Jul 29 23:16:07 EEST 2017

Hi, I was wondering if anyone has seen similar things. 

Trying 2 pass CBR or VBR in ffmpeg 

ffmpeg -I <input> -c:v libx264 -pass 1 -f mp4 /dev/null
ffmpeg -I <input> -c:v libx264 -b:v avg -maxrate max -minrate min -bufsize buf -pass 2 <output> 

appears to give bitrates that have peak deviations from the average of at least 40%. I tried making maxrate = minrate, 110% of it, removed minrate, removed maxrate, played with different bufsize (1 sec, 2 secs, 1/2 a sec, decreasing it makes the fluctuations smaller but still at 1/2 sec the deviations are large, at 1 sec they are up to 2x from the avg)

I tried multiple versions of ffmpeg and different clips. Is this is a known issue? 

Can anyone post an example of a case in which ffmpeg really gets CBR or say 110% VBR?


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