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Add variable alpha and size of half window for Kaiser-Bessel Derived window

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generation. Hard code Bessel I0 approximation iterations to 50.

See thread for discussion:
[FFmpeg-devel] [PATCH] Move Kaiser-Bessel Derived window to mdct.c
Started on the 2008/01/10

Originally committed as revision 11520 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Robert Swain 2008-01-13 11:02:08 +00:00
parent 99fac0806b
commit 3ed546fe52
3 changed files with 12 additions and 9 deletions
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2
libavcodec/ac3dec.c
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@ -277,7 +277,7 @@ static int ac3_decode_init(AVCodecContext *avctx)
ac3_tables_init();
ff_mdct_init(&s->imdct_256, 8, 1);
ff_mdct_init(&s->imdct_512, 9, 1);
ff_kbd_window_init(s->window);
ff_kbd_window_init(s->window, 5.0, 256);
dsputil_init(&s->dsp, avctx);
av_init_random(0, &s->dith_state);

4
libavcodec/dsputil.h
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@ -648,8 +648,10 @@ typedef struct MDCTContext {
/**
* Generate a Kaiser-Bessel Derived Window.
* @param window pointer to half window
* @param alpha determines window shape
* @param n size of half window
*/
void ff_kbd_window_init(float *window);
void ff_kbd_window_init(float *window, float alpha, int n);
int ff_mdct_init(MDCTContext *s, int nbits, int inverse);
void ff_imdct_calc(MDCTContext *s, FFTSample *output,

15
libavcodec/mdct.c
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@ -26,24 +26,25 @@
*/
// Generate a Kaiser-Bessel Derived Window.
void ff_kbd_window_init(float *window)
#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
void ff_kbd_window_init(float *window, float alpha, int n)
{
int i, j;
double sum = 0.0, bessel, tmp;
double local_window[256];
double alpha2 = (5.0 * M_PI / 256.0) * (5.0 * M_PI / 256.0);
double local_window[n];
double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
for (i = 0; i < 256; i++) {
tmp = i * (256 - i) * alpha2;
for (i = 0; i < n; i++) {
tmp = i * (n - i) * alpha2;
bessel = 1.0;
for (j = 100; j > 0; j--) /* default to 100 iterations */
for (j = BESSEL_I0_ITER; j > 0; j--)
bessel = bessel * tmp / (j * j) + 1;
sum += bessel;
local_window[i] = sum;
}
sum++;
for (i = 0; i < 256; i++)
for (i = 0; i < n; i++)
window[i] = sqrt(local_window[i] / sum);
}