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, band;
 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     bin  = start;
 110     band = bin_to_band_tab[start];
 111     do {
 112         int v = psd[bin++];
 113         int band_end = FFMIN(band_start_tab[band+1], end);
 114         for (; bin < band_end; bin++) {
 115             /* logadd */
 116             int adr = FFMIN(FFABS(v - psd[bin]) >> 1, 255);
 117             v = FFMAX(v, psd[bin]) + ff_ac3_log_add_tab[adr];
 118         }
 119         band_psd[band++] = v;
 120     } while (end > band_start_tab[band]);
 121 }
 122
 123 int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
 124                                int start, int end, int fast_gain, int is_lfe,
 125                                int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
 126                                uint8_t *dba_lengths, uint8_t *dba_values,
 127                                int16_t *mask)
 128 {
 129     int16_t excite[50]; /* excitation */
 130     int bin, k;
 131     int bndstrt, bndend, begin, end1, tmp;
 132     int lowcomp, fastleak, slowleak;
 133
 134     /* excitation function */
 135     bndstrt = bin_to_band_tab[start];
 136     bndend  = bin_to_band_tab[end-1] + 1;
 137
 138     if (bndstrt == 0) {
 139         lowcomp = 0;
 140         lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384);
 141         excite[0] = band_psd[0] - fast_gain - lowcomp;
 142         lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384);
 143         excite[1] = band_psd[1] - fast_gain - lowcomp;
 144         begin = 7;
 145         for (bin = 2; bin < 7; bin++) {
 146             if (!(is_lfe && bin == 6))
 147                 lowcomp = calc_lowcomp1(lowcomp, band_psd[bin], band_psd[bin+1], 384);
 148             fastleak = band_psd[bin] - fast_gain;
 149             slowleak = band_psd[bin] - s->slow_gain;
 150             excite[bin] = fastleak - lowcomp;
 151             if (!(is_lfe && bin == 6)) {
 152                 if (band_psd[bin] <= band_psd[bin+1]) {
 153                     begin = bin + 1;
 154                     break;
 155                 }
 156             }
 157         }
 158
 159         end1=bndend;
 160         if (end1 > 22) end1=22;
 161
 162         for (bin = begin; bin < end1; bin++) {
 163             if (!(is_lfe && bin == 6))
 164                 lowcomp = calc_lowcomp(lowcomp, band_psd[bin], band_psd[bin+1], bin);
 165
 166             fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);
 167             slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);
 168             excite[bin] = FFMAX(fastleak - lowcomp, slowleak);
 169         }
 170         begin = 22;
 171     } else {
 172         /* coupling channel */
 173         begin = bndstrt;
 174
 175         fastleak = (s->cpl_fast_leak << 8) + 768;
 176         slowleak = (s->cpl_slow_leak << 8) + 768;
 177     }
 178
 179     for (bin = begin; bin < bndend; bin++) {
 180         fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);
 181         slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);
 182         excite[bin] = FFMAX(fastleak, slowleak);
 183     }
 184
 185     /* compute masking curve */
 186
 187     for (bin = bndstrt; bin < bndend; bin++) {
 188         tmp = s->db_per_bit - band_psd[bin];
 189         if (tmp > 0) {
 190             excite[bin] += tmp >> 2;
 191         }
 192         mask[bin] = FFMAX(ff_ac3_hearing_threshold_tab[bin >> s->sr_shift][s->sr_code], excite[bin]);
 193     }
 194
 195     /* delta bit allocation */
 196
 197     if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
 198         int band, seg, delta;
 199         if (dba_nsegs >= 8)
 200             return -1;
 201         band = 0;
 202         for (seg = 0; seg < dba_nsegs; seg++) {
 203             band += dba_offsets[seg];
 204             if (band >= 50 || dba_lengths[seg] > 50-band)
 205                 return -1;
 206             if (dba_values[seg] >= 4) {
 207                 delta = (dba_values[seg] - 3) << 7;
 208             } else {
 209                 delta = (dba_values[seg] - 4) << 7;
 210             }
 211             for (k = 0; k < dba_lengths[seg]; k++) {
 212                 mask[band] += delta;
 213                 band++;
 214             }
 215         }
 216     }
 217     return 0;
 218 }
 219
 220 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
 221                                int snr_offset, int floor,
 222                                const uint8_t *bap_tab, uint8_t *bap)
 223 {
 224     int i, j, k, end1, v, address;
 225
 226     /* special case, if snr offset is -960, set all bap's to zero */
 227     if (snr_offset == -960) {
 228         memset(bap, 0, 256);
 229         return;
 230     }
 231
 232     i = start;
 233     j = bin_to_band_tab[start];
 234     do {
 235         v = (FFMAX(mask[j] - snr_offset - floor, 0) & 0x1FE0) + floor;
 236         end1 = FFMIN(band_start_tab[j] + ff_ac3_critical_band_size_tab[j], end);
 237         for (k = i; k < end1; k++) {
 238             address = av_clip((psd[i] - v) >> 5, 0, 63);
 239             bap[i] = bap_tab[address];
 240             i++;
 241         }
 242     } while (end > band_start_tab[j++]);
 243 }
 244
 245 /* AC-3 bit allocation. The algorithm is the one described in the AC-3
 246    spec. */
 247 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
 248                                    int8_t *exp, int start, int end,
 249                                    int snr_offset, int fast_gain, int is_lfe,
 250                                    int dba_mode, int dba_nsegs,
 251                                    uint8_t *dba_offsets, uint8_t *dba_lengths,
 252                                    uint8_t *dba_values)
 253 {
 254     int16_t psd[256];   /* scaled exponents */
 255     int16_t band_psd[50]; /* interpolated exponents */
 256     int16_t mask[50];   /* masking value */
 257
 258     ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd);
 259
 260     ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe,
 261                                dba_mode, dba_nsegs, dba_offsets, dba_lengths,
 262                                dba_values, mask);
 263
 264     ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor,
 265                               ff_ac3_bap_tab, bap);
 266 }
 267
 268 /**
 269  * Initializes some tables.
 270  * note: This function must remain thread safe because it is called by the
 271  *       AVParser init code.
 272  */
 273 av_cold void ac3_common_init(void)
 274 {
 275 #if !CONFIG_HARDCODED_TABLES
 276     int i, j, k, l, v;
 277     /* compute bndtab and masktab from bandsz */
 278     k = 0;
 279     l = 0;
 280     for (i = 0; i < 50; i++) {
 281         band_start_tab[i] = l;
 282         v = ff_ac3_critical_band_size_tab[i];
 283         for (j = 0; j < v; j++)
 284             bin_to_band_tab[k++] = i;
 285         l += v;
 286     }
 287     band_start_tab[50] = l;
 288 #endif /* !CONFIG_HARDCODED_TABLES */
 289 }