libavcodec/ac3.c

   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 "get_bits.h"
  30
  31 #if CONFIG_HARDCODED_TABLES
  32
  33 /**
  34  * Starting frequency coefficient bin for each critical band.
  35  */
  36 static const uint8_t band_start_tab[51] = {
  37       0,  1,   2,   3,   4,   5,   6,   7,   8,   9,
  38      10,  11, 12,  13,  14,  15,  16,  17,  18,  19,
  39      20,  21, 22,  23,  24,  25,  26,  27,  28,  31,
  40      34,  37, 40,  43,  46,  49,  55,  61,  67,  73,
  41      79,  85, 97, 109, 121, 133, 157, 181, 205, 229, 253
  42 };
  43
  44 /**
  45  * Maps each frequency coefficient bin to the critical band that contains it.
  46  */
  47 static const uint8_t bin_to_band_tab[253] = {
  48      0,
  49      1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12,
  50     13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
  51     25, 26, 27, 28, 28, 28, 29, 29, 29, 30, 30, 30,
  52     31, 31, 31, 32, 32, 32, 33, 33, 33, 34, 34, 34,
  53     35, 35, 35, 35, 35, 35, 36, 36, 36, 36, 36, 36,
  54     37, 37, 37, 37, 37, 37, 38, 38, 38, 38, 38, 38,
  55     39, 39, 39, 39, 39, 39, 40, 40, 40, 40, 40, 40,
  56     41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
  57     42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
  58     43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
  59     44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44,
  60     45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
  61     45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
  62     46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
  63     46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
  64     47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
  65     47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
  66     48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
  67     48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
  68     49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49,
  69     49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49
  70 };
  71
  72 #else /* CONFIG_HARDCODED_TABLES */
  73 static uint8_t band_start_tab[51];
  74 static uint8_t bin_to_band_tab[253];
  75 #endif
  76
  77 static inline int calc_lowcomp1(int a, int b0, int b1, int c)
  78 {
  79     if ((b0 + 256) == b1) {
  80         a = c;
  81     } else if (b0 > b1) {
  82         a = FFMAX(a - 64, 0);
  83     }
  84     return a;
  85 }
  86
  87 static inline int calc_lowcomp(int a, int b0, int b1, int bin)
  88 {
  89     if (bin < 7) {
  90         return calc_lowcomp1(a, b0, b1, 384);
  91     } else if (bin < 20) {
  92         return calc_lowcomp1(a, b0, b1, 320);
  93     } else {
  94         return FFMAX(a - 128, 0);
  95     }
  96 }
  97
  98 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
  99                                int16_t *band_psd)
 100 {
 101     int bin, i, j, k, end1, v;
 102
 103     /* exponent mapping to PSD */
 104     for(bin=start;bin<end;bin++) {
 105         psd[bin]=(3072 - (exp[bin] << 7));
 106     }
 107
 108     /* PSD integration */
 109     j=start;
 110     k=bin_to_band_tab[start];
 111     do {
 112         v=psd[j];
 113         j++;
 114         end1 = FFMIN(band_start_tab[k+1], end);
 115         for(i=j;i<end1;i++) {
 116             /* logadd */
 117             int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255);
 118             v = FFMAX(v, psd[j]) + ff_ac3_log_add_tab[adr];
 119             j++;
 120         }
 121         band_psd[k]=v;
 122         k++;
 123     } while (end > band_start_tab[k]);
 124 }
 125
 126 int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
 127                                int start, int end, int fast_gain, int is_lfe,
 128                                int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
 129                                uint8_t *dba_lengths, uint8_t *dba_values,
 130                                int16_t *mask)
 131 {
 132     int16_t excite[50]; /* excitation */
 133     int bin, k;
 134     int bndstrt, bndend, begin, end1, tmp;
 135     int lowcomp, fastleak, slowleak;
 136
 137     /* excitation function */
 138     bndstrt = bin_to_band_tab[start];
 139     bndend = bin_to_band_tab[end-1] + 1;
 140
 141     if (bndstrt == 0) {
 142         lowcomp = 0;
 143         lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384);
 144         excite[0] = band_psd[0] - fast_gain - lowcomp;
 145         lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384);
 146         excite[1] = band_psd[1] - fast_gain - lowcomp;
 147         begin = 7;
 148         for (bin = 2; bin < 7; bin++) {
 149             if (!(is_lfe && bin == 6))
 150                 lowcomp = calc_lowcomp1(lowcomp, band_psd[bin], band_psd[bin+1], 384);
 151             fastleak = band_psd[bin] - fast_gain;
 152             slowleak = band_psd[bin] - s->slow_gain;
 153             excite[bin] = fastleak - lowcomp;
 154             if (!(is_lfe && bin == 6)) {
 155                 if (band_psd[bin] <= band_psd[bin+1]) {
 156                     begin = bin + 1;
 157                     break;
 158                 }
 159             }
 160         }
 161
 162         end1=bndend;
 163         if (end1 > 22) end1=22;
 164
 165         for (bin = begin; bin < end1; bin++) {
 166             if (!(is_lfe && bin == 6))
 167                 lowcomp = calc_lowcomp(lowcomp, band_psd[bin], band_psd[bin+1], bin);
 168
 169             fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);
 170             slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);
 171             excite[bin] = FFMAX(fastleak - lowcomp, slowleak);
 172         }
 173         begin = 22;
 174     } else {
 175         /* coupling channel */
 176         begin = bndstrt;
 177
 178         fastleak = (s->cpl_fast_leak << 8) + 768;
 179         slowleak = (s->cpl_slow_leak << 8) + 768;
 180     }
 181
 182     for (bin = begin; bin < bndend; bin++) {
 183         fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);
 184         slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);
 185         excite[bin] = FFMAX(fastleak, slowleak);
 186     }
 187
 188     /* compute masking curve */
 189
 190     for (bin = bndstrt; bin < bndend; bin++) {
 191         tmp = s->db_per_bit - band_psd[bin];
 192         if (tmp > 0) {
 193             excite[bin] += tmp >> 2;
 194         }
 195         mask[bin] = FFMAX(ff_ac3_hearing_threshold_tab[bin >> s->sr_shift][s->sr_code], excite[bin]);
 196     }
 197
 198     /* delta bit allocation */
 199
 200     if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
 201         int band, seg, delta;
 202         if (dba_nsegs >= 8)
 203             return -1;
 204         band = 0;
 205         for (seg = 0; seg < dba_nsegs; seg++) {
 206             band += dba_offsets[seg];
 207             if (band >= 50 || dba_lengths[seg] > 50-band)
 208                 return -1;
 209             if (dba_values[seg] >= 4) {
 210                 delta = (dba_values[seg] - 3) << 7;
 211             } else {
 212                 delta = (dba_values[seg] - 4) << 7;
 213             }
 214             for (k = 0; k < dba_lengths[seg]; k++) {
 215                 mask[band] += delta;
 216                 band++;
 217             }
 218         }
 219     }
 220     return 0;
 221 }
 222
 223 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
 224                                int snr_offset, int floor,
 225                                const uint8_t *bap_tab, uint8_t *bap)
 226 {
 227     int i, j, k, end1, v, address;
 228
 229     /* special case, if snr offset is -960, set all bap's to zero */
 230     if(snr_offset == -960) {
 231         memset(bap, 0, 256);
 232         return;
 233     }
 234
 235     i = start;
 236     j = bin_to_band_tab[start];
 237     do {
 238         v = (FFMAX(mask[j] - snr_offset - floor, 0) & 0x1FE0) + floor;
 239         end1 = FFMIN(band_start_tab[j] + ff_ac3_critical_band_size_tab[j], end);
 240         for (k = i; k < end1; k++) {
 241             address = av_clip((psd[i] - v) >> 5, 0, 63);
 242             bap[i] = bap_tab[address];
 243             i++;
 244         }
 245     } while (end > band_start_tab[j++]);
 246 }
 247
 248 /* AC-3 bit allocation. The algorithm is the one described in the AC-3
 249    spec. */
 250 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
 251                                    int8_t *exp, int start, int end,
 252                                    int snr_offset, int fast_gain, int is_lfe,
 253                                    int dba_mode, int dba_nsegs,
 254                                    uint8_t *dba_offsets, uint8_t *dba_lengths,
 255                                    uint8_t *dba_values)
 256 {
 257     int16_t psd[256];   /* scaled exponents */
 258     int16_t band_psd[50]; /* interpolated exponents */
 259     int16_t mask[50];   /* masking value */
 260
 261     ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd);
 262
 263     ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe,
 264                                dba_mode, dba_nsegs, dba_offsets, dba_lengths, dba_values,
 265                                mask);
 266
 267     ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor,
 268                               ff_ac3_bap_tab, bap);
 269 }
 270
 271 /**
 272  * Initializes some tables.
 273  * note: This function must remain thread safe because it is called by the
 274  *       AVParser init code.
 275  */
 276 av_cold void ac3_common_init(void)
 277 {
 278 #if !CONFIG_HARDCODED_TABLES
 279     int i, j, k, l, v;
 280     /* compute bndtab and masktab from bandsz */
 281     k = 0;
 282     l = 0;
 283     for(i=0;i<50;i++) {
 284         band_start_tab[i] = l;
 285         v = ff_ac3_critical_band_size_tab[i];
 286         for(j=0;j<v;j++) bin_to_band_tab[k++]=i;
 287         l += v;
 288     }
 289     band_start_tab[50] = l;
 290 #endif /* !CONFIG_HARDCODED_TABLES */
 291 }