3 * Copyright (c) 2006 Justin Ruggles <justin.ruggles@gmail.com>
5 * This file is part of FFmpeg.
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.
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.
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
22 #include "libavutil/common.h"
23 #include "libavutil/lls.h"
25 #define LPC_USE_DOUBLE
27 #include "libavutil/avassert.h"
31 * Apply Welch window function to audio block
33 static void lpc_apply_welch_window_c(const int32_t *data, int len,
40 /* The optimization in commit fa4ed8c does not support odd len.
41 * If someone wants odd len extend that change. */
42 av_assert2(!(len & 1));
45 c = 2.0 / (len - 1.0);
52 w_data[-i-1] = data[-i-1] * w;
53 w_data[+i ] = data[+i ] * w;
58 * Calculate autocorrelation data from audio samples
59 * A Welch window function is applied before calculation.
61 static void lpc_compute_autocorr_c(const double *data, int len, int lag,
66 for(j=0; j<lag; j+=2){
67 double sum0 = 1.0, sum1 = 1.0;
69 sum0 += data[i] * data[i-j];
70 sum1 += data[i] * data[i-j-1];
78 for(i=j-1; i<len; i+=2){
79 sum += data[i ] * data[i-j ]
80 + data[i+1] * data[i-j+1];
87 * Quantize LPC coefficients
89 static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
90 int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
97 /* define maximum levels */
98 qmax = (1 << (precision - 1)) - 1;
100 /* find maximum coefficient value */
102 for(i=0; i<order; i++) {
103 cmax= FFMAX(cmax, fabs(lpc_in[i]));
106 /* if maximum value quantizes to zero, return all zeros */
107 if(cmax * (1 << max_shift) < 1.0) {
109 memset(lpc_out, 0, sizeof(int32_t) * order);
113 /* calculate level shift which scales max coeff to available bits */
115 while((cmax * (1 << sh) > qmax) && (sh > 0)) {
119 /* since negative shift values are unsupported in decoder, scale down
120 coefficients instead */
121 if(sh == 0 && cmax > qmax) {
122 double scale = ((double)qmax) / cmax;
123 for(i=0; i<order; i++) {
128 /* output quantized coefficients and level shift */
130 for(i=0; i<order; i++) {
131 error -= lpc_in[i] * (1 << sh);
132 lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
138 static int estimate_best_order(double *ref, int min_order, int max_order)
143 for(i=max_order-1; i>=min_order-1; i--) {
153 * Calculate LPC coefficients for multiple orders
155 * @param lpc_type LPC method for determining coefficients,
156 * see #FFLPCType for details
158 int ff_lpc_calc_coefs(LPCContext *s,
159 const int32_t *samples, int blocksize, int min_order,
160 int max_order, int precision,
161 int32_t coefs[][MAX_LPC_ORDER], int *shift,
162 enum FFLPCType lpc_type, int lpc_passes,
163 int omethod, int max_shift, int zero_shift)
165 double autoc[MAX_LPC_ORDER+1];
166 double ref[MAX_LPC_ORDER];
167 double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
171 av_assert2(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER &&
172 lpc_type > FF_LPC_TYPE_FIXED);
174 /* reinit LPC context if parameters have changed */
175 if (blocksize != s->blocksize || max_order != s->max_order ||
176 lpc_type != s->lpc_type) {
178 ff_lpc_init(s, blocksize, max_order, lpc_type);
181 if (lpc_type == FF_LPC_TYPE_LEVINSON) {
182 double *windowed_samples = s->windowed_samples + max_order;
184 s->lpc_apply_welch_window(samples, blocksize, windowed_samples);
186 s->lpc_compute_autocorr(windowed_samples, blocksize, max_order, autoc);
188 compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
190 for(i=0; i<max_order; i++)
191 ref[i] = fabs(lpc[i][i]);
192 } else if (lpc_type == FF_LPC_TYPE_CHOLESKY) {
194 double var[MAX_LPC_ORDER+1], av_uninit(weight);
199 for(pass=0; pass<lpc_passes; pass++){
200 av_init_lls(&m[pass&1], max_order);
203 for(i=max_order; i<blocksize; i++){
204 for(j=0; j<=max_order; j++)
205 var[j]= samples[i-j];
208 double eval, inv, rinv;
209 eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
210 eval= (512>>pass) + fabs(eval - var[0]);
213 for(j=0; j<=max_order; j++)
219 av_update_lls(&m[pass&1], var, 1.0);
221 av_solve_lls(&m[pass&1], 0.001, 0);
224 for(i=0; i<max_order; i++){
225 for(j=0; j<max_order; j++)
226 lpc[i][j]=-m[(pass-1)&1].coeff[i][j];
227 ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
229 for(i=max_order-1; i>0; i--)
230 ref[i] = ref[i-1] - ref[i];
232 opt_order = max_order;
234 if(omethod == ORDER_METHOD_EST) {
235 opt_order = estimate_best_order(ref, min_order, max_order);
237 quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
239 for(i=min_order-1; i<max_order; i++) {
240 quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
247 av_cold int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
248 enum FFLPCType lpc_type)
250 s->blocksize = blocksize;
251 s->max_order = max_order;
252 s->lpc_type = lpc_type;
254 if (lpc_type == FF_LPC_TYPE_LEVINSON) {
255 s->windowed_samples = av_mallocz((blocksize + max_order + 2) *
256 sizeof(*s->windowed_samples));
257 if (!s->windowed_samples)
258 return AVERROR(ENOMEM);
260 s->windowed_samples = NULL;
263 s->lpc_apply_welch_window = lpc_apply_welch_window_c;
264 s->lpc_compute_autocorr = lpc_compute_autocorr_c;
272 av_cold void ff_lpc_end(LPCContext *s)
274 av_freep(&s->windowed_samples);