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
28 #define ORDER_METHOD_EST 0
29 #define ORDER_METHOD_2LEVEL 1
30 #define ORDER_METHOD_4LEVEL 2
31 #define ORDER_METHOD_8LEVEL 3
32 #define ORDER_METHOD_SEARCH 4
33 #define ORDER_METHOD_LOG 5
35 #define MIN_LPC_ORDER 1
36 #define MAX_LPC_ORDER 32
39 typedef struct LPCContext {
42 enum AVLPCType lpc_type;
43 double *windowed_samples;
46 * Apply a Welch window to an array of input samples.
47 * The output samples have the same scale as the input, but are in double
49 * @param data input samples
50 * @param len number of input samples
51 * @param w_data output samples
53 void (*lpc_apply_welch_window)(const int32_t *data, int len,
56 * Perform autocorrelation on input samples with delay of 0 to lag.
57 * @param data input samples.
58 * constraints: no alignment needed, but must have have at
59 * least lag*sizeof(double) valid bytes preceeding it, and
60 * size must be at least (len+1)*sizeof(double) if data is
61 * 16-byte aligned or (len+2)*sizeof(double) if data is
63 * @param len number of input samples to process
64 * @param lag maximum delay to calculate
65 * @param autoc output autocorrelation coefficients.
66 * constraints: array size must be at least lag+1.
68 void (*lpc_compute_autocorr)(const double *data, int len, int lag,
74 * Calculate LPC coefficients for multiple orders
76 int ff_lpc_calc_coefs(LPCContext *s,
77 const int32_t *samples, int blocksize, int min_order,
78 int max_order, int precision,
79 int32_t coefs[][MAX_LPC_ORDER], int *shift,
80 enum AVLPCType lpc_type, int lpc_passes,
81 int omethod, int max_shift, int zero_shift);
84 * Initialize LPCContext.
86 int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
87 enum AVLPCType lpc_type);
88 void ff_lpc_init_x86(LPCContext *s);
91 * Uninitialize LPCContext.
93 void ff_lpc_end(LPCContext *s);
96 #define LPC_TYPE double
98 #define LPC_TYPE float
102 * Levinson-Durbin recursion.
103 * Produce LPC coefficients from autocorrelation data.
105 static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
106 LPC_TYPE *lpc, int lpc_stride, int fail,
111 LPC_TYPE *lpc_last = lpc;
116 if (fail && (autoc[max_order - 1] == 0 || err <= 0))
119 for(i=0; i<max_order; i++) {
120 LPC_TYPE r = -autoc[i];
124 r -= lpc_last[j] * autoc[i-j-1];
127 err *= 1.0 - (r * r);
132 for(j=0; j < (i+1)>>1; j++) {
133 LPC_TYPE f = lpc_last[ j];
134 LPC_TYPE b = lpc_last[i-1-j];
136 lpc[i-1-j] = b + r * f;
149 #endif /* AVCODEC_LPC_H */