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Add biquad high-pass and low-pass IIR filters.

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Signed-off-by: Mans Rullgard <mans@mansr.com>
This commit is contained in:
Justin Ruggles 2011-01-20 21:26:47 +00:00 committed by Mans Rullgard
parent 66c6b5e2a5
commit fcdf0a43cd
2 changed files with 51 additions and 0 deletions
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50
libavcodec/iirfilter.c
View File

@ -112,6 +112,51 @@ static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
return 0;
}
static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
enum IIRFilterMode filt_mode, int order,
float cutoff_ratio, float stopband)
{
double cos_w0, sin_w0;
double a0, x0, x1;
if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
filt_mode != FF_FILTER_MODE_LOWPASS) {
av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
"high-pass and low-pass filter modes\n");
return -1;
}
if (order != 2) {
av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
return -1;
}
cos_w0 = cos(M_PI * cutoff_ratio);
sin_w0 = sin(M_PI * cutoff_ratio);
a0 = 1.0 + (sin_w0 / 2.0);
if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
c->gain = ((1.0 + cos_w0) / 2.0) / a0;
x0 = (-(1.0 + cos_w0)) / a0;
x1 = ((1.0 + cos_w0) / 2.0) / a0;
} else { // FF_FILTER_MODE_LOWPASS
c->gain = ((1.0 - cos_w0) / 2.0) / a0;
x0 = (1.0 - cos_w0) / a0;
x1 = ((1.0 - cos_w0) / 2.0) / a0;
}
c->cy[0] = (2.0 * cos_w0) / a0;
c->cy[1] = (-1.0 + (sin_w0 / 2.0)) / a0;
// divide by gain to make the x coeffs integers.
// during filtering, the delay state will include the gain multiplication
c->cx[0] = lrintf(x0 / c->gain);
c->cx[1] = lrintf(x1 / c->gain);
c->cy[0] /= c->gain;
c->cy[1] /= c->gain;
return 0;
}
av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
enum IIRFilterType filt_type,
enum IIRFilterMode filt_mode,
@ -136,6 +181,11 @@ av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
stopband)) {
goto init_fail;
}
} else if (filt_type == FF_FILTER_TYPE_BIQUAD) {
if (biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
stopband)) {
goto init_fail;
}
} else {
av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
goto init_fail;

1
libavcodec/iirfilter.h
View File

@ -34,6 +34,7 @@ struct FFIIRFilterState;
enum IIRFilterType{
FF_FILTER_TYPE_BESSEL,
FF_FILTER_TYPE_BIQUAD,
FF_FILTER_TYPE_BUTTERWORTH,
FF_FILTER_TYPE_CHEBYSHEV,
FF_FILTER_TYPE_ELLIPTIC,