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avfilter/f_ebur128: use transformed direct form II

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Instead of direct form I. See af_biquads.c for math. Also eliminate
an unnecessary indirection.
This commit is contained in:
Niklas Haas
2025-06-12 17:42:37 +02:00
parent 8aa6df663e
commit c5f3033a86
1 changed files with 5 additions and 7 deletions
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12
libavfilter/f_ebur128.c
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@ -686,17 +686,15 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
/* Y[i] = X[i]*b0 + X[i-1]*b1 + X[i-2]*b2 - Y[i-1]*a1 - Y[i-2]*a2 */
#define FILTER(Y, X, NUM, DEN) do { \
double *dst = ebur128->Y + ch*3; \
double *src = ebur128->X + ch*3; \
dst[2] = dst[1]; \
dst[1] = dst[0]; \
dst[0] = src[0]*NUM[0] + src[1]*NUM[1] + src[2]*NUM[2] \
- dst[1]*DEN[1] - dst[2]*DEN[2]; \
double src = ebur128->X[ch*3] ; \
double dst0 = NUM[0] * src + dst[1]; \
dst[1] = NUM[1] * src + dst[2] - DEN[1] * dst0; \
dst[2] = NUM[2] * src - DEN[2] * dst0; \
dst[0] = dst0; \
} while (0)
// TODO: merge both filters in one?
FILTER(y, x, ebur128->pre_b, ebur128->pre_a); // apply pre-filter
ebur128->x[ch * 3 + 2] = ebur128->x[ch * 3 + 1];
ebur128->x[ch * 3 + 1] = ebur128->x[ch * 3 ];
FILTER(z, y, ebur128->rlb_b, ebur128->rlb_a); // apply RLB-filter
bin = ebur128->z[ch * 3] * ebur128->z[ch * 3];