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

[Francois Visagie]

> -----Original Message-----
> From: ffmpeg-user-bounces at ffmpeg.org [mailto:ffmpeg-user-
> bounces at ffmpeg.org] On Behalf Of Nicolas George
> Sent: 14 August 2013 16:45
> To: FFmpeg user questions
> Subject: Re: [FFmpeg-user] Preserving perceived loudness when
> downmixing audio from 5.1 AC3 to stereo AAC
> 
> 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.

Thank you.

Kind regards,
Francois