1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
|
/**
* LPC utility code
* Copyright (c) 2006 Justin Ruggles <justin.ruggles@gmail.com>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "libavutil/lls.h"
#include "dsputil.h"
#include "lpc.h"
/**
* Levinson-Durbin recursion.
* Produces LPC coefficients from autocorrelation data.
*/
static void compute_lpc_coefs(const double *autoc, int max_order,
double lpc[][MAX_LPC_ORDER], double *ref)
{
int i, j, i2;
double r, err, tmp;
double lpc_tmp[MAX_LPC_ORDER];
for(i=0; i<max_order; i++) lpc_tmp[i] = 0;
err = autoc[0];
for(i=0; i<max_order; i++) {
r = -autoc[i+1];
for(j=0; j<i; j++) {
r -= lpc_tmp[j] * autoc[i-j];
}
r /= err;
ref[i] = fabs(r);
err *= 1.0 - (r * r);
i2 = (i >> 1);
lpc_tmp[i] = r;
for(j=0; j<i2; j++) {
tmp = lpc_tmp[j];
lpc_tmp[j] += r * lpc_tmp[i-1-j];
lpc_tmp[i-1-j] += r * tmp;
}
if(i & 1) {
lpc_tmp[j] += lpc_tmp[j] * r;
}
for(j=0; j<=i; j++) {
lpc[i][j] = -lpc_tmp[j];
}
}
}
/**
* Quantize LPC coefficients
*/
static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
{
int i;
double cmax, error;
int32_t qmax;
int sh;
/* define maximum levels */
qmax = (1 << (precision - 1)) - 1;
/* find maximum coefficient value */
cmax = 0.0;
for(i=0; i<order; i++) {
cmax= FFMAX(cmax, fabs(lpc_in[i]));
}
/* if maximum value quantizes to zero, return all zeros */
if(cmax * (1 << max_shift) < 1.0) {
*shift = zero_shift;
memset(lpc_out, 0, sizeof(int32_t) * order);
return;
}
/* calculate level shift which scales max coeff to available bits */
sh = max_shift;
while((cmax * (1 << sh) > qmax) && (sh > 0)) {
sh--;
}
/* since negative shift values are unsupported in decoder, scale down
coefficients instead */
if(sh == 0 && cmax > qmax) {
double scale = ((double)qmax) / cmax;
for(i=0; i<order; i++) {
lpc_in[i] *= scale;
}
}
/* output quantized coefficients and level shift */
error=0;
for(i=0; i<order; i++) {
error += lpc_in[i] * (1 << sh);
lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
error -= lpc_out[i];
}
*shift = sh;
}
static int estimate_best_order(double *ref, int min_order, int max_order)
{
int i, est;
est = min_order;
for(i=max_order-1; i>=min_order-1; i--) {
if(ref[i] > 0.10) {
est = i+1;
break;
}
}
return est;
}
/**
* Calculate LPC coefficients for multiple orders
*/
int ff_lpc_calc_coefs(DSPContext *s,
const int32_t *samples, int blocksize, int min_order,
int max_order, int precision,
int32_t coefs[][MAX_LPC_ORDER], int *shift, int use_lpc,
int omethod, int max_shift, int zero_shift)
{
double autoc[MAX_LPC_ORDER+1];
double ref[MAX_LPC_ORDER];
double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
int i, j, pass;
int opt_order;
assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER);
if(use_lpc == 1){
s->flac_compute_autocorr(samples, blocksize, max_order, autoc);
compute_lpc_coefs(autoc, max_order, lpc, ref);
}else{
LLSModel m[2];
double var[MAX_LPC_ORDER+1], 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){
double eval, inv, rinv;
eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
eval= (512>>pass) + fabs(eval - var[0]);
inv = 1/eval;
rinv = sqrt(inv);
for(j=0; j<=max_order; j++)
var[j] *= rinv;
weight += inv;
}else
weight++;
av_update_lls(&m[pass&1], var, 1.0);
}
av_solve_lls(&m[pass&1], 0.001, 0);
}
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 = max_order;
if(omethod == ORDER_METHOD_EST) {
opt_order = estimate_best_order(ref, min_order, max_order);
i = opt_order-1;
quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
} else {
for(i=min_order-1; i<max_order; i++) {
quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
}
}
return opt_order;
}
|
