/* * LPC utility code * Copyright (c) 2006 Justin Ruggles <justin.ruggles@gmail.com> * * This file is part of Libav. * * Libav 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. * * Libav 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 Libav; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #ifndef AVCODEC_LPC_H #define AVCODEC_LPC_H #include <stdint.h> #define ORDER_METHOD_EST 0 #define ORDER_METHOD_2LEVEL 1 #define ORDER_METHOD_4LEVEL 2 #define ORDER_METHOD_8LEVEL 3 #define ORDER_METHOD_SEARCH 4 #define ORDER_METHOD_LOG 5 #define MIN_LPC_ORDER 1 #define MAX_LPC_ORDER 32 /** * LPC analysis type */ enum FFLPCType { FF_LPC_TYPE_DEFAULT = -1, ///< use the codec default LPC type FF_LPC_TYPE_NONE = 0, ///< do not use LPC prediction or use all zero coefficients FF_LPC_TYPE_FIXED = 1, ///< fixed LPC coefficients FF_LPC_TYPE_LEVINSON = 2, ///< Levinson-Durbin recursion FF_LPC_TYPE_CHOLESKY = 3, ///< Cholesky factorization FF_LPC_TYPE_NB , ///< Not part of ABI }; typedef struct LPCContext { int blocksize; int max_order; enum FFLPCType lpc_type; double *windowed_buffer; double *windowed_samples; /** * Apply a Welch window to an array of input samples. * The output samples have the same scale as the input, but are in double * sample format. * @param data input samples * @param len number of input samples * @param w_data output samples */ void (*lpc_apply_welch_window)(const int32_t *data, int len, double *w_data); /** * Perform autocorrelation on input samples with delay of 0 to lag. * @param data input samples. * constraints: no alignment needed, but must have have at * least lag*sizeof(double) valid bytes preceding it, and * size must be at least (len+1)*sizeof(double) if data is * 16-byte aligned or (len+2)*sizeof(double) if data is * unaligned. * @param len number of input samples to process * @param lag maximum delay to calculate * @param autoc output autocorrelation coefficients. * constraints: array size must be at least lag+1. */ void (*lpc_compute_autocorr)(const double *data, int len, int lag, double *autoc); } LPCContext; /** * Calculate LPC coefficients for multiple orders */ int ff_lpc_calc_coefs(LPCContext *s, const int32_t *samples, int blocksize, int min_order, int max_order, int precision, int32_t coefs[][MAX_LPC_ORDER], int *shift, enum FFLPCType lpc_type, int lpc_passes, int omethod, int max_shift, int zero_shift); int ff_lpc_calc_ref_coefs(LPCContext *s, const int32_t *samples, int order, double *ref); /** * Initialize LPCContext. */ int ff_lpc_init(LPCContext *s, int blocksize, int max_order, enum FFLPCType lpc_type); void ff_lpc_init_x86(LPCContext *s); /** * Uninitialize LPCContext. */ void ff_lpc_end(LPCContext *s); #ifdef LPC_USE_DOUBLE #define LPC_TYPE double #else #define LPC_TYPE float #endif /** * Schur recursion. * Produces reflection coefficients from autocorrelation data. */ static inline void compute_ref_coefs(const LPC_TYPE *autoc, int max_order, LPC_TYPE *ref, LPC_TYPE *error) { int i, j; LPC_TYPE err; LPC_TYPE gen0[MAX_LPC_ORDER], gen1[MAX_LPC_ORDER]; for (i = 0; i < max_order; i++) gen0[i] = gen1[i] = autoc[i + 1]; err = autoc[0]; ref[0] = -gen1[0] / err; err += gen1[0] * ref[0]; if (error) error[0] = err; for (i = 1; i < max_order; i++) { for (j = 0; j < max_order - i; j++) { gen1[j] = gen1[j + 1] + ref[i - 1] * gen0[j]; gen0[j] = gen1[j + 1] * ref[i - 1] + gen0[j]; } ref[i] = -gen1[0] / err; err += gen1[0] * ref[i]; if (error) error[i] = err; } } /** * Levinson-Durbin recursion. * Produce LPC coefficients from autocorrelation data. */ static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order, LPC_TYPE *lpc, int lpc_stride, int fail, int normalize) { int i, j; LPC_TYPE err = 0; LPC_TYPE *lpc_last = lpc; if (normalize) err = *autoc++; if (fail && (autoc[max_order - 1] == 0 || err <= 0)) return -1; for(i=0; i<max_order; i++) { LPC_TYPE r = -autoc[i]; if (normalize) { for(j=0; j<i; j++) r -= lpc_last[j] * autoc[i-j-1]; r /= err; err *= 1.0 - (r * r); } lpc[i] = r; for(j=0; j < (i+1)>>1; j++) { LPC_TYPE f = lpc_last[ j]; LPC_TYPE b = lpc_last[i-1-j]; lpc[ j] = f + r * b; lpc[i-1-j] = b + r * f; } if (fail && err < 0) return -1; lpc_last = lpc; lpc += lpc_stride; } return 0; } #endif /* AVCODEC_LPC_H */