1/* 2 * Common code between the AC-3 encoder and decoder 3 * Copyright (c) 2000 Fabrice Bellard 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/** 23 * @file libavcodec/ac3.c 24 * Common code between the AC-3 encoder and decoder. 25 */ 26 27#include "avcodec.h" 28#include "ac3.h" 29#include "bitstream.h" 30 31static uint8_t band_start_tab[51]; 32static uint8_t bin_to_band_tab[253]; 33 34static inline int calc_lowcomp1(int a, int b0, int b1, int c) 35{ 36 if ((b0 + 256) == b1) { 37 a = c; 38 } else if (b0 > b1) { 39 a = FFMAX(a - 64, 0); 40 } 41 return a; 42} 43 44static inline int calc_lowcomp(int a, int b0, int b1, int bin) 45{ 46 if (bin < 7) { 47 return calc_lowcomp1(a, b0, b1, 384); 48 } else if (bin < 20) { 49 return calc_lowcomp1(a, b0, b1, 320); 50 } else { 51 return FFMAX(a - 128, 0); 52 } 53} 54 55void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd, 56 int16_t *band_psd) 57{ 58 int bin, i, j, k, end1, v; 59 60 /* exponent mapping to PSD */ 61 for(bin=start;bin<end;bin++) { 62 psd[bin]=(3072 - (exp[bin] << 7)); 63 } 64 65 /* PSD integration */ 66 j=start; 67 k=bin_to_band_tab[start]; 68 do { 69 v=psd[j]; 70 j++; 71 end1 = FFMIN(band_start_tab[k+1], end); 72 for(i=j;i<end1;i++) { 73 /* logadd */ 74 int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255); 75 v = FFMAX(v, psd[j]) + ff_ac3_log_add_tab[adr]; 76 j++; 77 } 78 band_psd[k]=v; 79 k++; 80 } while (end > band_start_tab[k]); 81} 82 83int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd, 84 int start, int end, int fast_gain, int is_lfe, 85 int dba_mode, int dba_nsegs, uint8_t *dba_offsets, 86 uint8_t *dba_lengths, uint8_t *dba_values, 87 int16_t *mask) 88{ 89 int16_t excite[50]; /* excitation */ 90 int bin, k; 91 int bndstrt, bndend, begin, end1, tmp; 92 int lowcomp, fastleak, slowleak; 93 94 /* excitation function */ 95 bndstrt = bin_to_band_tab[start]; 96 bndend = bin_to_band_tab[end-1] + 1; 97 98 if (bndstrt == 0) { 99 lowcomp = 0; 100 lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384); 101 excite[0] = band_psd[0] - fast_gain - lowcomp; 102 lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384); 103 excite[1] = band_psd[1] - fast_gain - lowcomp; 104 begin = 7; 105 for (bin = 2; bin < 7; bin++) { 106 if (!(is_lfe && bin == 6)) 107 lowcomp = calc_lowcomp1(lowcomp, band_psd[bin], band_psd[bin+1], 384); 108 fastleak = band_psd[bin] - fast_gain; 109 slowleak = band_psd[bin] - s->slow_gain; 110 excite[bin] = fastleak - lowcomp; 111 if (!(is_lfe && bin == 6)) { 112 if (band_psd[bin] <= band_psd[bin+1]) { 113 begin = bin + 1; 114 break; 115 } 116 } 117 } 118 119 end1=bndend; 120 if (end1 > 22) end1=22; 121 122 for (bin = begin; bin < end1; bin++) { 123 if (!(is_lfe && bin == 6)) 124 lowcomp = calc_lowcomp(lowcomp, band_psd[bin], band_psd[bin+1], bin); 125 126 fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain); 127 slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain); 128 excite[bin] = FFMAX(fastleak - lowcomp, slowleak); 129 } 130 begin = 22; 131 } else { 132 /* coupling channel */ 133 begin = bndstrt; 134 135 fastleak = (s->cpl_fast_leak << 8) + 768; 136 slowleak = (s->cpl_slow_leak << 8) + 768; 137 } 138 139 for (bin = begin; bin < bndend; bin++) { 140 fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain); 141 slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain); 142 excite[bin] = FFMAX(fastleak, slowleak); 143 } 144 145 /* compute masking curve */ 146 147 for (bin = bndstrt; bin < bndend; bin++) { 148 tmp = s->db_per_bit - band_psd[bin]; 149 if (tmp > 0) { 150 excite[bin] += tmp >> 2; 151 } 152 mask[bin] = FFMAX(ff_ac3_hearing_threshold_tab[bin >> s->sr_shift][s->sr_code], excite[bin]); 153 } 154 155 /* delta bit allocation */ 156 157 if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) { 158 int band, seg, delta; 159 if (dba_nsegs >= 8) 160 return -1; 161 band = 0; 162 for (seg = 0; seg < dba_nsegs; seg++) { 163 band += dba_offsets[seg]; 164 if (band >= 50 || dba_lengths[seg] > 50-band) 165 return -1; 166 if (dba_values[seg] >= 4) { 167 delta = (dba_values[seg] - 3) << 7; 168 } else { 169 delta = (dba_values[seg] - 4) << 7; 170 } 171 for (k = 0; k < dba_lengths[seg]; k++) { 172 mask[band] += delta; 173 band++; 174 } 175 } 176 } 177 return 0; 178} 179 180void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end, 181 int snr_offset, int floor, 182 const uint8_t *bap_tab, uint8_t *bap) 183{ 184 int i, j, k, end1, v, address; 185 186 /* special case, if snr offset is -960, set all bap's to zero */ 187 if(snr_offset == -960) { 188 memset(bap, 0, 256); 189 return; 190 } 191 192 i = start; 193 j = bin_to_band_tab[start]; 194 do { 195 v = (FFMAX(mask[j] - snr_offset - floor, 0) & 0x1FE0) + floor; 196 end1 = FFMIN(band_start_tab[j] + ff_ac3_critical_band_size_tab[j], end); 197 for (k = i; k < end1; k++) { 198 address = av_clip((psd[i] - v) >> 5, 0, 63); 199 bap[i] = bap_tab[address]; 200 i++; 201 } 202 } while (end > band_start_tab[j++]); 203} 204 205/* AC-3 bit allocation. The algorithm is the one described in the AC-3 206 spec. */ 207void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap, 208 int8_t *exp, int start, int end, 209 int snr_offset, int fast_gain, int is_lfe, 210 int dba_mode, int dba_nsegs, 211 uint8_t *dba_offsets, uint8_t *dba_lengths, 212 uint8_t *dba_values) 213{ 214 int16_t psd[256]; /* scaled exponents */ 215 int16_t band_psd[50]; /* interpolated exponents */ 216 int16_t mask[50]; /* masking value */ 217 218 ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd); 219 220 ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe, 221 dba_mode, dba_nsegs, dba_offsets, dba_lengths, dba_values, 222 mask); 223 224 ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor, 225 ff_ac3_bap_tab, bap); 226} 227 228/** 229 * Initializes some tables. 230 * note: This function must remain thread safe because it is called by the 231 * AVParser init code. 232 */ 233av_cold void ac3_common_init(void) 234{ 235 int i, j, k, l, v; 236 /* compute bndtab and masktab from bandsz */ 237 k = 0; 238 l = 0; 239 for(i=0;i<50;i++) { 240 band_start_tab[i] = l; 241 v = ff_ac3_critical_band_size_tab[i]; 242 for(j=0;j<v;j++) bin_to_band_tab[k++]=i; 243 l += v; 244 } 245 band_start_tab[50] = l; 246} 247