[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 14:44:02 CEST 2013

Le septidi 27 thermidor, an CCXXI, Francois Visagie a écrit :
> Is it possible to normalise audio levels using ffmpeg? The 'pan' filter
> documentation mentions:

Define "normalize".

> "If the ‘=’ in a channel specification is replaced by ‘<’, then the gains
> for that specification will be renormalized so that the total is 1, thus
> avoiding clipping noise."

Read carefully: "so that the total is 1", "avoiding clipping". That is
exactly what was discussed in this thread.

> I.e., having downmixed to stereo, can one expect correct normalisation
> from '-filter:a pan=stereo:c0<c0:c1<c1'?

This filter does nothing, obviously.

> If not, does ffmpeg provide a better mechanism, or is something like that
> in planning?

There are mechanism, they are mostly good, but you are not specific enough.


  Nicolas George
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