[FFmpeg-user] Preserving perceived loudness when downmixing audio from 5.1 AC3 to stereo AAC

Nicolas George nicolas.george at normalesup.org
Wed Aug 14 16:44:59 CEST 2013

Le septidi 27 thermidor, an CCXXI, Francois Visagie a écrit :
> Apologies, I do not know enough about this field to express myself
> clearly. I'll try to improve: I'm looking for an ffmpeg mechanism that
> automatically determines and uniformly applies to the audio stream a gain
> factor that ensures maximum output levels without clipping.

What you are looking for is the output of volumedetect. See the
documentation for explanations on what every field means.

>							      An added
> benefit would be the ability to specify the maximum permitted output level
> as a percentage of maximum possible output level.

volumedetect provides the mean volume of the file, you can do the arithmetic
from there. ebur128 provides a more realistic measure of the mean volume,
but it is slower.

Any such method requires two passes to work correctly, since volume peaks
can be present at the very end of the stream.


  Nicolas George
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