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ac3.c
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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
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 }
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