[FFmpeg-devel] [PATCH] Lowpass functionality for lavc

[Michael Niedermayer]

On Tue, Aug 12, 2008 at 02:23:55PM +0300, Kostya wrote:
> $subj, made as a separate module.

[...]

> /**
>  * Initialize filter coefficients.
>  *
>  * @param coeffs filter coefficients
>  * @param freq   input frequency (sample rate/2)
>  * @param cutoff cutoff frequency
>  *
>  * @return zero if filter creation succeeded, a negative value if filter could not be created
>  */
> int ff_lowpass_filter_init_coeffs(LPFilterCoeffs *coeffs, int freq, int cutoff);

the filter order should also be a parameter


> 
> /**
>  * Filter input value.
>  *
>  * @param coeffs filter coefficients
>  * @param s      filter state
>  * @param in     input value
>  *
>  * @return filtered value
>  */
> static av_always_inline float ff_lowpass_filter(LPFilterCoeffs *coeffs, LPFilterState *s, float in)
> {
>     int i;
>     for(i = 0; i < LOWPASS_FILTER_ORDER; i++){
>         s->x[i] = s->x[i+1];
>         s->y[i] = s->y[i+1];
>     }
>     s->x[LOWPASS_FILTER_ORDER] = in * coeffs->gain;
>     //FIXME: made only for 4th order filter
>     s->y[LOWPASS_FILTER_ORDER] = (s->x[0] + s->x[4])*1
>                                + (s->x[1] + s->x[3])*4
>                                +  s->x[2]           *6
>                                + coeffs->c[0]*s->y[0] + coeffs->c[1]*s->y[1]
>                                + coeffs->c[2]*s->y[2] + coeffs->c[3]*s->y[3];
>     return s->y[LOWPASS_FILTER_ORDER];
> }

as already said in my other reply this should be unrolled so it needs no
moving of samples.



> int ff_lowpass_filter_init_coeffs(LPFilterCoeffs *coeffs, int freq, int cutoff)
> {
>     int i, j, size;
>     float cutoff_ratio;
> 

>     //since I'm too lazy to calculate coefficients, I take more or less matching ones from the table
>     //TODO: generic version

hmm


-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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