[Ffmpeg-devel] alsa input / output

[Michael Niedermayer]

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(???)... :)

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
3. multiply coefficients with the correct constants (this if iam not too
   tired just multiplies coeffs with 0 or 1)
4. IFFT
5. downsample by throwing away the right samples

and yes there are certainly much more efficient ways to implement it, i
just wanted to demonstrate the low asymptotic complexity

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

The educated differ from the uneducated as much as the living from the
dead. -- Aristotle 
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