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 Libav.
   6  *
   7  * Libav 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  * Libav 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 Libav; 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
  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 /**
  32  * Starting frequency coefficient bin for each critical band.
  33  */
  34 const uint8_t ff_ac3_band_start_tab[AC3_CRITICAL_BANDS+1] = {
  35       0,  1,   2,   3,   4,   5,   6,   7,   8,   9,
  36      10,  11, 12,  13,  14,  15,  16,  17,  18,  19,
  37      20,  21, 22,  23,  24,  25,  26,  27,  28,  31,
  38      34,  37, 40,  43,  46,  49,  55,  61,  67,  73,
  39      79,  85, 97, 109, 121, 133, 157, 181, 205, 229, 253
  40 };
  41
  42 #if CONFIG_HARDCODED_TABLES
  43
  44 /**
  45  * Map each frequency coefficient bin to the critical band that contains it.
  46  */
  47 const uint8_t ff_ac3_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 uint8_t ff_ac3_bin_to_band_tab[253];
  74 #endif
  75
  76 static inline int calc_lowcomp1(int a, int b0, int b1, int c)
  77 {
  78     if ((b0 + 256) == b1) {
  79         a = c;
  80     } else if (b0 > b1) {
  81         a = FFMAX(a - 64, 0);
  82     }
  83     return a;
  84 }
  85
  86 static inline int calc_lowcomp(int a, int b0, int b1, int bin)
  87 {
  88     if (bin < 7) {
  89         return calc_lowcomp1(a, b0, b1, 384);
  90     } else if (bin < 20) {
  91         return calc_lowcomp1(a, b0, b1, 320);
  92     } else {
  93         return FFMAX(a - 128, 0);
  94     }
  95 }
  96
  97 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
  98                                int16_t *band_psd)
  99 {
 100     int bin, band;
 101
 102     /* exponent mapping to PSD */
 103     for (bin = start; bin < end; bin++) {
 104         psd[bin]=(3072 - (exp[bin] << 7));
 105     }
 106
 107     /* PSD integration */
 108     bin  = start;
 109     band = ff_ac3_bin_to_band_tab[start];
 110     do {
 111         int v = psd[bin++];
 112         int band_end = FFMIN(ff_ac3_band_start_tab[band+1], end);
 113         for (; bin < band_end; bin++) {
 114             int max = FFMAX(v, psd[bin]);
 115             /* logadd */
 116             int adr = FFMIN(max - ((v + psd[bin] + 1) >> 1), 255);
 117             v = max + ff_ac3_log_add_tab[adr];
 118         }
 119         band_psd[band++] = v;
 120     } while (end > ff_ac3_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[AC3_CRITICAL_BANDS]; /* excitation */
 130     int band;
 131     int band_start, band_end, begin, end1;
 132     int lowcomp, fastleak, slowleak;
 133
 134     /* excitation function */
 135     band_start = ff_ac3_bin_to_band_tab[start];
 136     band_end   = ff_ac3_bin_to_band_tab[end-1] + 1;
 137
 138     if (band_start == 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 (band = 2; band < 7; band++) {
 146             if (!(is_lfe && band == 6))
 147                 lowcomp = calc_lowcomp1(lowcomp, band_psd[band], band_psd[band+1], 384);
 148             fastleak = band_psd[band] - fast_gain;
 149             slowleak = band_psd[band] - s->slow_gain;
 150             excite[band] = fastleak - lowcomp;
 151             if (!(is_lfe && band == 6)) {
 152                 if (band_psd[band] <= band_psd[band+1]) {
 153                     begin = band + 1;
 154                     break;
 155                 }
 156             }
 157         }
 158
 159         end1 = FFMIN(band_end, 22);
 160         for (band = begin; band < end1; band++) {
 161             if (!(is_lfe && band == 6))
 162                 lowcomp = calc_lowcomp(lowcomp, band_psd[band], band_psd[band+1], band);
 163             fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
 164             slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
 165             excite[band] = FFMAX(fastleak - lowcomp, slowleak);
 166         }
 167         begin = 22;
 168     } else {
 169         /* coupling channel */
 170         begin = band_start;
 171         fastleak = (s->cpl_fast_leak << 8) + 768;
 172         slowleak = (s->cpl_slow_leak << 8) + 768;
 173     }
 174
 175     for (band = begin; band < band_end; band++) {
 176         fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
 177         slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
 178         excite[band] = FFMAX(fastleak, slowleak);
 179     }
 180
 181     /* compute masking curve */
 182
 183     for (band = band_start; band < band_end; band++) {
 184         int tmp = s->db_per_bit - band_psd[band];
 185         if (tmp > 0) {
 186             excite[band] += tmp >> 2;
 187         }
 188         mask[band] = FFMAX(ff_ac3_hearing_threshold_tab[band >> s->sr_shift][s->sr_code], excite[band]);
 189     }
 190
 191     /* delta bit allocation */
 192
 193     if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
 194         int i, seg, delta;
 195         if (dba_nsegs > 8)
 196             return -1;
 197         band = band_start;
 198         for (seg = 0; seg < dba_nsegs; seg++) {
 199             band += dba_offsets[seg];
 200             if (band >= AC3_CRITICAL_BANDS || dba_lengths[seg] > AC3_CRITICAL_BANDS-band)
 201                 return -1;
 202             if (dba_values[seg] >= 4) {
 203                 delta = (dba_values[seg] - 3) << 7;
 204             } else {
 205                 delta = (dba_values[seg] - 4) << 7;
 206             }
 207             for (i = 0; i < dba_lengths[seg]; i++) {
 208                 mask[band++] += delta;
 209             }
 210         }
 211     }
 212     return 0;
 213 }
 214
 215 /**
 216  * Initialize some tables.
 217  * note: This function must remain thread safe because it is called by the
 218  *       AVParser init code.
 219  */
 220 av_cold void ff_ac3_common_init(void)
 221 {
 222 #if !CONFIG_HARDCODED_TABLES
 223     /* compute ff_ac3_bin_to_band_tab from ff_ac3_band_start_tab */
 224     int bin = 0, band;
 225     for (band = 0; band < AC3_CRITICAL_BANDS; band++) {
 226         int band_end = ff_ac3_band_start_tab[band+1];
 227         while (bin < band_end)
 228             ff_ac3_bin_to_band_tab[bin++] = band;
 229     }
 230 #endif /* !CONFIG_HARDCODED_TABLES */
 231 }