[FFmpeg-devel] [PATCH] Support for reducing from 5.1 and 4.0audio?to stereo audio

Michael Niedermayer michaelni
Wed Oct 31 22:36:37 CET 2007

On Wed, Oct 31, 2007 at 11:01:14PM +0200, Jan Knutar wrote:
> On Wednesday 31 October 2007 22:41, Rich Felker wrote:
> > Clipping is just as bad as overflow...

no, cliping by +-1 is not as bad as a +-1 overflow
if its +-10000 then yes sure cliping is as bad

> > Anyway this is not a digital mixing console, it's a fully automated
> > process which has to avoid doing things which are fundamentally wrong
> > even if they do preserve more dynamic range in certain situations.
> > Degrading information gracefully (which a filter like this should be
> > expected to do anyway!) is nothing like applying massive distortions
> > to the spectrum.
> The poor user can always compensate by turning the volume up, and suffer 
> the tiny little extra noise... But how does one compensate for the 
> argh-my-ears-are-bleeding sensation that clipping causes? :)

turn the volume down before the downmixing ;)

anyway the question really is how big the maximum amplitude is after
the downmixing but before the downscaling with valid streams
if any cliping by more then 1% is needed then the samples must be
downscaled more to avoid that
or to say it differently if theres nothing in the codec specs which
gurantees that the sum of channels fits in 16bit then we must downscale
well unless someone finally implements 32bit audio support

also some formats can store downmixing coeffs and such which might be
helpfull here.

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I do not agree with what you have to say, but I'll defend to the death your
right to say it. -- Voltaire
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