[Ffmpeg-devel] alsa input / output

Rich Felker dalias
Wed Mar 21 07:09:41 CET 2007


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. :(

> 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.

Rich




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