Statistics
| Branch: | Revision:

ffmpeg / libavcodec / lpc.c @ 9045f5e7

History | View | Annotate | Download (5.71 KB)

1
/**
2
 * LPC utility code
3
 * Copyright (c) 2006  Justin Ruggles <jruggle@earthlink.net>
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
#include "lpc.h"
25

    
26

    
27
/**
28
 * Levinson-Durbin recursion.
29
 * Produces LPC coefficients from autocorrelation data.
30
 */
31
static void compute_lpc_coefs(const double *autoc, int max_order,
32
                              double lpc[][MAX_LPC_ORDER], double *ref)
33
{
34
   int i, j, i2;
35
   double r, err, tmp;
36
   double lpc_tmp[MAX_LPC_ORDER];
37

    
38
   for(i=0; i<max_order; i++) lpc_tmp[i] = 0;
39
   err = autoc[0];
40

    
41
   for(i=0; i<max_order; i++) {
42
      r = -autoc[i+1];
43
      for(j=0; j<i; j++) {
44
          r -= lpc_tmp[j] * autoc[i-j];
45
      }
46
      r /= err;
47
      ref[i] = fabs(r);
48

    
49
      err *= 1.0 - (r * r);
50

    
51
      i2 = (i >> 1);
52
      lpc_tmp[i] = r;
53
      for(j=0; j<i2; j++) {
54
         tmp = lpc_tmp[j];
55
         lpc_tmp[j] += r * lpc_tmp[i-1-j];
56
         lpc_tmp[i-1-j] += r * tmp;
57
      }
58
      if(i & 1) {
59
          lpc_tmp[j] += lpc_tmp[j] * r;
60
      }
61

    
62
      for(j=0; j<=i; j++) {
63
          lpc[i][j] = -lpc_tmp[j];
64
      }
65
   }
66
}
67

    
68
/**
69
 * Quantize LPC coefficients
70
 */
71
static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
72
                               int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
73
{
74
    int i;
75
    double cmax, error;
76
    int32_t qmax;
77
    int sh;
78

    
79
    /* define maximum levels */
80
    qmax = (1 << (precision - 1)) - 1;
81

    
82
    /* find maximum coefficient value */
83
    cmax = 0.0;
84
    for(i=0; i<order; i++) {
85
        cmax= FFMAX(cmax, fabs(lpc_in[i]));
86
    }
87

    
88
    /* if maximum value quantizes to zero, return all zeros */
89
    if(cmax * (1 << max_shift) < 1.0) {
90
        *shift = zero_shift;
91
        memset(lpc_out, 0, sizeof(int32_t) * order);
92
        return;
93
    }
94

    
95
    /* calculate level shift which scales max coeff to available bits */
96
    sh = max_shift;
97
    while((cmax * (1 << sh) > qmax) && (sh > 0)) {
98
        sh--;
99
    }
100

    
101
    /* since negative shift values are unsupported in decoder, scale down
102
       coefficients instead */
103
    if(sh == 0 && cmax > qmax) {
104
        double scale = ((double)qmax) / cmax;
105
        for(i=0; i<order; i++) {
106
            lpc_in[i] *= scale;
107
        }
108
    }
109

    
110
    /* output quantized coefficients and level shift */
111
    error=0;
112
    for(i=0; i<order; i++) {
113
        error += lpc_in[i] * (1 << sh);
114
        lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
115
        error -= lpc_out[i];
116
    }
117
    *shift = sh;
118
}
119

    
120
static int estimate_best_order(double *ref, int max_order)
121
{
122
    int i, est;
123

    
124
    est = 1;
125
    for(i=max_order-1; i>=0; i--) {
126
        if(ref[i] > 0.10) {
127
            est = i+1;
128
            break;
129
        }
130
    }
131
    return est;
132
}
133

    
134
/**
135
 * Calculate LPC coefficients for multiple orders
136
 */
137
int ff_lpc_calc_coefs(DSPContext *s,
138
                      const int32_t *samples, int blocksize, int min_order,
139
                      int max_order, int precision,
140
                      int32_t coefs[][MAX_LPC_ORDER], int *shift, int use_lpc,
141
                      int omethod, int max_shift, int zero_shift)
142
{
143
    double autoc[MAX_LPC_ORDER+1];
144
    double ref[MAX_LPC_ORDER];
145
    double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
146
    int i, j, pass;
147
    int opt_order;
148

    
149
    assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER);
150

    
151
    if(use_lpc == 1){
152
        s->flac_compute_autocorr(samples, blocksize, max_order, autoc);
153

    
154
        compute_lpc_coefs(autoc, max_order, lpc, ref);
155
    }else{
156
        LLSModel m[2];
157
        double var[MAX_LPC_ORDER+1], weight;
158

    
159
        for(pass=0; pass<use_lpc-1; pass++){
160
            av_init_lls(&m[pass&1], max_order);
161

    
162
            weight=0;
163
            for(i=max_order; i<blocksize; i++){
164
                for(j=0; j<=max_order; j++)
165
                    var[j]= samples[i-j];
166

    
167
                if(pass){
168
                    double eval, inv, rinv;
169
                    eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
170
                    eval= (512>>pass) + fabs(eval - var[0]);
171
                    inv = 1/eval;
172
                    rinv = sqrt(inv);
173
                    for(j=0; j<=max_order; j++)
174
                        var[j] *= rinv;
175
                    weight += inv;
176
                }else
177
                    weight++;
178

    
179
                av_update_lls(&m[pass&1], var, 1.0);
180
            }
181
            av_solve_lls(&m[pass&1], 0.001, 0);
182
        }
183

    
184
        for(i=0; i<max_order; i++){
185
            for(j=0; j<max_order; j++)
186
                lpc[i][j]= m[(pass-1)&1].coeff[i][j];
187
            ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
188
        }
189
        for(i=max_order-1; i>0; i--)
190
            ref[i] = ref[i-1] - ref[i];
191
    }
192
    opt_order = max_order;
193

    
194
    if(omethod == ORDER_METHOD_EST) {
195
        opt_order = estimate_best_order(ref, max_order);
196
        i = opt_order-1;
197
        quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
198
    } else {
199
        for(i=min_order-1; i<max_order; i++) {
200
            quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
201
        }
202
    }
203

    
204
    return opt_order;
205
}