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calculate all coefficients for several orders during cholesky factorization, the resulting coefficients are not strictly optimal though as there is a small difference in the autocorrelation matrixes which is ignored for the smaller orders

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Originally committed as revision 5758 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer
2006-07-15 23:43:38 +00:00
parent 6ce704bbed
commit 408ec4e2a6
3 changed files with 55 additions and 40 deletions
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24
libavcodec/flacenc.c
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@@ -742,35 +742,41 @@ static int lpc_calc_coefs(const int32_t *samples, int blocksize, int max_order,
compute_autocorr(samples, blocksize, max_order+1, autoc);
compute_lpc_coefs(autoc, max_order, lpc, ref);
opt_order = estimate_best_order(ref, max_order);
}else{
LLSModel m[2];
double var[MAX_LPC_ORDER+1], eval;
double var[MAX_LPC_ORDER+1], eval, weight;
for(pass=0; pass<use_lpc-1; pass++){
av_init_lls(&m[pass&1], max_order);
weight=0;
for(i=max_order; i<blocksize; i++){
for(j=0; j<=max_order; j++)
var[j]= samples[i-j];
if(pass){
eval= av_evaluate_lls(&m[(pass-1)&1], var+1);
eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
eval= (512>>pass) + fabs(eval - var[0]);
for(j=0; j<=max_order; j++)
var[j]/= sqrt(eval);
}
weight += 1/eval;
}else
weight++;
av_update_lls(&m[pass&1], var, 1.0);
}
av_solve_lls(&m[pass&1], 0.001);
opt_order= max_order; //FIXME
av_solve_lls(&m[pass&1], 0.001, 0);
}
for(i=0; i<opt_order; i++)
lpc[opt_order-1][i]= m[(pass-1)&1].coeff[i];
for(i=0; i<max_order; i++){
for(j=0; j<max_order; j++)
lpc[i][j]= m[(pass-1)&1].coeff[i][j];
ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
}
for(i=max_order-1; i>0; i--)
ref[i] = ref[i-1] - ref[i];
}
opt_order = estimate_best_order(ref, max_order);
i = opt_order-1;
quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i]);