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#ifndef AVCODEC_LPC_H 23#define AVCODEC_LPC_H 24 25#include <stdint.h> 26#include "libavutil/avassert.h" 27 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 34 35#define MIN_LPC_ORDER 1 36#define MAX_LPC_ORDER 32 37 38/** 39 * LPC analysis type 40 */ 41enum FFLPCType { 42 FF_LPC_TYPE_DEFAULT = -1, ///< use the codec default LPC type 43 FF_LPC_TYPE_NONE = 0, ///< do not use LPC prediction or use all zero coefficients 44 FF_LPC_TYPE_FIXED = 1, ///< fixed LPC coefficients 45 FF_LPC_TYPE_LEVINSON = 2, ///< Levinson-Durbin recursion 46 FF_LPC_TYPE_CHOLESKY = 3, ///< Cholesky factorization 47 FF_LPC_TYPE_NB , ///< Not part of ABI 48}; 49 50typedef struct LPCContext { 51 int blocksize; 52 int max_order; 53 enum FFLPCType lpc_type; 54 double *windowed_buffer; 55 double *windowed_samples; 56 57 /** 58 * Apply a Welch window to an array of input samples. 59 * The output samples have the same scale as the input, but are in double 60 * sample format. 61 * @param data input samples 62 * @param len number of input samples 63 * @param w_data output samples 64 */ 65 void (*lpc_apply_welch_window)(const int32_t *data, int len, 66 double *w_data); 67 /** 68 * Perform autocorrelation on input samples with delay of 0 to lag. 69 * @param data input samples. 70 * constraints: no alignment needed, but must have at 71 * least lag*sizeof(double) valid bytes preceding it, and 72 * size must be at least (len+1)*sizeof(double) if data is 73 * 16-byte aligned or (len+2)*sizeof(double) if data is 74 * unaligned. 75 * @param len number of input samples to process 76 * @param lag maximum delay to calculate 77 * @param autoc output autocorrelation coefficients. 78 * constraints: array size must be at least lag+1. 79 */ 80 void (*lpc_compute_autocorr)(const double *data, int len, int lag, 81 double *autoc); 82} LPCContext; 83 84 85/** 86 * Calculate LPC coefficients for multiple orders 87 */ 88int ff_lpc_calc_coefs(LPCContext *s, 89 const int32_t *samples, int blocksize, int min_order, 90 int max_order, int precision, 91 int32_t coefs[][MAX_LPC_ORDER], int *shift, 92 enum FFLPCType lpc_type, int lpc_passes, 93 int omethod, int max_shift, int zero_shift); 94 95int ff_lpc_calc_ref_coefs(LPCContext *s, 96 const int32_t *samples, int order, double *ref); 97 98/** 99 * Initialize LPCContext. 100 */ 101int ff_lpc_init(LPCContext *s, int blocksize, int max_order, 102 enum FFLPCType lpc_type); 103void ff_lpc_init_x86(LPCContext *s); 104 105/** 106 * Uninitialize LPCContext. 107 */ 108void ff_lpc_end(LPCContext *s); 109 110#ifdef LPC_USE_DOUBLE 111#define LPC_TYPE double 112#else 113#define LPC_TYPE float 114#endif 115 116/** 117 * Schur recursion. 118 * Produces reflection coefficients from autocorrelation data. 119 */ 120static inline void compute_ref_coefs(const LPC_TYPE *autoc, int max_order, 121 LPC_TYPE *ref, LPC_TYPE *error) 122{ 123 int i, j; 124 LPC_TYPE err; 125 LPC_TYPE gen0[MAX_LPC_ORDER], gen1[MAX_LPC_ORDER]; 126 127 for (i = 0; i < max_order; i++) 128 gen0[i] = gen1[i] = autoc[i + 1]; 129 130 err = autoc[0]; 131 ref[0] = -gen1[0] / err; 132 err += gen1[0] * ref[0]; 133 if (error) 134 error[0] = err; 135 for (i = 1; i < max_order; i++) { 136 for (j = 0; j < max_order - i; j++) { 137 gen1[j] = gen1[j + 1] + ref[i - 1] * gen0[j]; 138 gen0[j] = gen1[j + 1] * ref[i - 1] + gen0[j]; 139 } 140 ref[i] = -gen1[0] / err; 141 err += gen1[0] * ref[i]; 142 if (error) 143 error[i] = err; 144 } 145} 146 147/** 148 * Levinson-Durbin recursion. 149 * Produce LPC coefficients from autocorrelation data. 150 */ 151static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order, 152 LPC_TYPE *lpc, int lpc_stride, int fail, 153 int normalize) 154{ 155 int i, j; 156 LPC_TYPE err; 157 LPC_TYPE *lpc_last = lpc; 158 159 av_assert2(normalize || !fail); 160 161 if (normalize) 162 err = *autoc++; 163 164 if (fail && (autoc[max_order - 1] == 0 || err <= 0)) 165 return -1; 166 167 for(i=0; i<max_order; i++) { 168 LPC_TYPE r = -autoc[i]; 169 170 if (normalize) { 171 for(j=0; j<i; j++) 172 r -= lpc_last[j] * autoc[i-j-1]; 173 174 r /= err; 175 err *= 1.0 - (r * r); 176 } 177 178 lpc[i] = r; 179 180 for(j=0; j < (i+1)>>1; j++) { 181 LPC_TYPE f = lpc_last[ j]; 182 LPC_TYPE b = lpc_last[i-1-j]; 183 lpc[ j] = f + r * b; 184 lpc[i-1-j] = b + r * f; 185 } 186 187 if (fail && err < 0) 188 return -1; 189 190 lpc_last = lpc; 191 lpc += lpc_stride; 192 } 193 194 return 0; 195} 196 197#endif /* AVCODEC_LPC_H */ 198