[Ffmpeg-devel] alsa input / output

Michael Niedermayer michaelni
Wed Mar 21 12:12:26 CET 2007


Hi

On Wed, Mar 21, 2007 at 01:09:41AM -0500, Rich Felker wrote:
> On Wed, Mar 21, 2007 at 04:13:10AM +0100, Michael Niedermayer wrote:
> > Hi
> > 
> > On Tue, Mar 20, 2007 at 09:42:38PM -0500, Rich Felker wrote:
> > > On Wed, Mar 21, 2007 at 12:52:47AM +0000, M?ns Rullg?rd wrote:
> > > > Assuming the input is not undersampled, is there not exactly one
> > > > mathematically correct resampling?  It's been a while since I studied
> > > > signal processing, so I may have forgotten something.
> > > 
> > > Yes. Unfortunately it's O(???)... :)
> 
> Your (broken? weird that it becomes 3 ?'s and not just 1..) charset
> config lost the infinity. :(

yes yes i know my system is missconfigured ...


> 
> > if the ratio of the sample rates is rational (and constant relative to n)
> > then this can trivially be done in O(n*log n)
> > 1. upsample by adding zeros to the least common multiple of the samplerates
> >   (slow and silly but just adds a constant factor C*n)
> > 2. FFT
> 
> M?ns said the mathematically correct resampling. For this, the FT (and
> IFT) are infinite processes. What you describe is a finite
> approximation of it.

you dont have an infinite number of input samples you have n also they are
not at infinite precission but rather fixed point values and no matter 
how many n or how many bits of precission you can perform FFT/IFFT on
them if needed with arbitrary precission math. if
you now consider the increasing complexity of the arbitrary precission
stuff as n grows then you need to add a log n or log log n term but its
nowhere near infinity

the O(infinity) argument could be applied to any problem which doesnt
have a exact integer or rational solution

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The worst form of inequality is to try to make unequal things equal.
-- Aristotle
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