libavcodec/lpc.c

   1 /**
   2  * LPC utility code
   3  * Copyright (c) 2006  Justin Ruggles <justin.ruggles@gmail.com>
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 #include "libavutil/lls.h"
  23 #include "dsputil.h"
  24
  25 #define LPC_USE_DOUBLE
  26 #include "lpc.h"
  27
  28
  29 /**
  30  * Quantize LPC coefficients
  31  */
  32 static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
  33                                int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
  34 {
  35     int i;
  36     double cmax, error;
  37     int32_t qmax;
  38     int sh;
  39
  40     /* define maximum levels */
  41     qmax = (1 << (precision - 1)) - 1;
  42
  43     /* find maximum coefficient value */
  44     cmax = 0.0;
  45     for(i=0; i<order; i++) {
  46         cmax= FFMAX(cmax, fabs(lpc_in[i]));
  47     }
  48
  49     /* if maximum value quantizes to zero, return all zeros */
  50     if(cmax * (1 << max_shift) < 1.0) {
  51         *shift = zero_shift;
  52         memset(lpc_out, 0, sizeof(int32_t) * order);
  53         return;
  54     }
  55
  56     /* calculate level shift which scales max coeff to available bits */
  57     sh = max_shift;
  58     while((cmax * (1 << sh) > qmax) && (sh > 0)) {
  59         sh--;
  60     }
  61
  62     /* since negative shift values are unsupported in decoder, scale down
  63        coefficients instead */
  64     if(sh == 0 && cmax > qmax) {
  65         double scale = ((double)qmax) / cmax;
  66         for(i=0; i<order; i++) {
  67             lpc_in[i] *= scale;
  68         }
  69     }
  70
  71     /* output quantized coefficients and level shift */
  72     error=0;
  73     for(i=0; i<order; i++) {
  74         error -= lpc_in[i] * (1 << sh);
  75         lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
  76         error -= lpc_out[i];
  77     }
  78     *shift = sh;
  79 }
  80
  81 static int estimate_best_order(double *ref, int min_order, int max_order)
  82 {
  83     int i, est;
  84
  85     est = min_order;
  86     for(i=max_order-1; i>=min_order-1; i--) {
  87         if(ref[i] > 0.10) {
  88             est = i+1;
  89             break;
  90         }
  91     }
  92     return est;
  93 }
  94
  95 /**
  96  * Calculate LPC coefficients for multiple orders
  97  *
  98  * @param use_lpc LPC method for determining coefficients
  99  * 0  = LPC with fixed pre-defined coeffs
 100  * 1  = LPC with coeffs determined by Levinson-Durbin recursion
 101  * 2+ = LPC with coeffs determined by Cholesky factorization using (use_lpc-1) passes.
 102  */
 103 int ff_lpc_calc_coefs(DSPContext *s,
 104                       const int32_t *samples, int blocksize, int min_order,
 105                       int max_order, int precision,
 106                       int32_t coefs[][MAX_LPC_ORDER], int *shift, int use_lpc,
 107                       int omethod, int max_shift, int zero_shift)
 108 {
 109     double autoc[MAX_LPC_ORDER+1];
 110     double ref[MAX_LPC_ORDER];
 111     double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
 112     int i, j, pass;
 113     int opt_order;
 114
 115     assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER && use_lpc > 0);
 116
 117     if(use_lpc == 1){
 118         s->flac_compute_autocorr(samples, blocksize, max_order, autoc);
 119
 120         compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
 121
 122         for(i=0; i<max_order; i++)
 123             ref[i] = fabs(lpc[i][i]);
 124     }else{
 125         LLSModel m[2];
 126         double var[MAX_LPC_ORDER+1], av_uninit(weight);
 127
 128         for(pass=0; pass<use_lpc-1; pass++){
 129             av_init_lls(&m[pass&1], max_order);
 130
 131             weight=0;
 132             for(i=max_order; i<blocksize; i++){
 133                 for(j=0; j<=max_order; j++)
 134                     var[j]= samples[i-j];
 135
 136                 if(pass){
 137                     double eval, inv, rinv;
 138                     eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
 139                     eval= (512>>pass) + fabs(eval - var[0]);
 140                     inv = 1/eval;
 141                     rinv = sqrt(inv);
 142                     for(j=0; j<=max_order; j++)
 143                         var[j] *= rinv;
 144                     weight += inv;
 145                 }else
 146                     weight++;
 147
 148                 av_update_lls(&m[pass&1], var, 1.0);
 149             }
 150             av_solve_lls(&m[pass&1], 0.001, 0);
 151         }
 152
 153         for(i=0; i<max_order; i++){
 154             for(j=0; j<max_order; j++)
 155                 lpc[i][j]=-m[(pass-1)&1].coeff[i][j];
 156             ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
 157         }
 158         for(i=max_order-1; i>0; i--)
 159             ref[i] = ref[i-1] - ref[i];
 160     }
 161     opt_order = max_order;
 162
 163     if(omethod == ORDER_METHOD_EST) {
 164         opt_order = estimate_best_order(ref, min_order, max_order);
 165         i = opt_order-1;
 166         quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
 167     } else {
 168         for(i=min_order-1; i<max_order; i++) {
 169             quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
 170         }
 171     }
 172
 173     return opt_order;
 174 }