libavcodec/ac3.c

   1 /*
   2  * Common code between AC3 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 ac3.c
  24  * Common code between AC3 encoder and decoder.
  25  */
  26
  27 #include "avcodec.h"
  28 #include "ac3.h"
  29 #include "bitstream.h"
  30
  31 static uint8_t band_start_tab[51];
  32 static uint8_t bin_to_band_tab[253];
  33
  34 static 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
  44 static 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
  55 void 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
  83 void 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         band = 0;
 160         for (seg = 0; seg < dba_nsegs; seg++) {
 161             band += dba_offsets[seg];
 162             if (dba_values[seg] >= 4) {
 163                 delta = (dba_values[seg] - 3) << 7;
 164             } else {
 165                 delta = (dba_values[seg] - 4) << 7;
 166             }
 167             for (k = 0; k < dba_lengths[seg]; k++) {
 168                 mask[band] += delta;
 169                 band++;
 170             }
 171         }
 172     }
 173 }
 174
 175 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
 176                                int snr_offset, int floor, uint8_t *bap)
 177 {
 178     int i, j, k, end1, v, address;
 179
 180     /* special case, if snr offset is -960, set all bap's to zero */
 181     if(snr_offset == -960) {
 182         memset(bap, 0, 256);
 183         return;
 184     }
 185
 186     i = start;
 187     j = bin_to_band_tab[start];
 188     do {
 189         v = (FFMAX(mask[j] - snr_offset - floor, 0) & 0x1FE0) + floor;
 190         end1 = FFMIN(band_start_tab[j] + ff_ac3_critical_band_size_tab[j], end);
 191         for (k = i; k < end1; k++) {
 192             address = av_clip((psd[i] - v) >> 5, 0, 63);
 193             bap[i] = ff_ac3_bap_tab[address];
 194             i++;
 195         }
 196     } while (end > band_start_tab[j++]);
 197 }
 198
 199 /* AC3 bit allocation. The algorithm is the one described in the AC3
 200    spec. */
 201 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
 202                                    int8_t *exp, int start, int end,
 203                                    int snr_offset, int fast_gain, int is_lfe,
 204                                    int dba_mode, int dba_nsegs,
 205                                    uint8_t *dba_offsets, uint8_t *dba_lengths,
 206                                    uint8_t *dba_values)
 207 {
 208     int16_t psd[256];   /* scaled exponents */
 209     int16_t band_psd[50]; /* interpolated exponents */
 210     int16_t mask[50];   /* masking value */
 211
 212     ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd);
 213
 214     ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe,
 215                                dba_mode, dba_nsegs, dba_offsets, dba_lengths, dba_values,
 216                                mask);
 217
 218     ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor, bap);
 219 }
 220
 221 /**
 222  * Initializes some tables.
 223  * note: This function must remain thread safe because it is called by the
 224  *       AVParser init code.
 225  */
 226 av_cold void ac3_common_init(void)
 227 {
 228     int i, j, k, l, v;
 229     /* compute bndtab and masktab from bandsz */
 230     k = 0;
 231     l = 0;
 232     for(i=0;i<50;i++) {
 233         band_start_tab[i] = l;
 234         v = ff_ac3_critical_band_size_tab[i];
 235         for(j=0;j<v;j++) bin_to_band_tab[k++]=i;
 236         l += v;
 237     }
 238     band_start_tab[50] = l;
 239 }