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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  */
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 */
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;
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 
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  if (end <= 0)
135  return AVERROR_INVALIDDATA;
136 
137  /* excitation function */
138  band_start = ff_ac3_bin_to_band_tab[start];
139  band_end = ff_ac3_bin_to_band_tab[end-1] + 1;
140 
141  if (band_start == 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 (band = 2; band < 7; band++) {
149  if (!(is_lfe && band == 6))
150  lowcomp = calc_lowcomp1(lowcomp, band_psd[band], band_psd[band+1], 384);
151  fastleak = band_psd[band] - fast_gain;
152  slowleak = band_psd[band] - s->slow_gain;
153  excite[band] = fastleak - lowcomp;
154  if (!(is_lfe && band == 6)) {
155  if (band_psd[band] <= band_psd[band+1]) {
156  begin = band + 1;
157  break;
158  }
159  }
160  }
161 
162  end1 = FFMIN(band_end, 22);
163  for (band = begin; band < end1; band++) {
164  if (!(is_lfe && band == 6))
165  lowcomp = calc_lowcomp(lowcomp, band_psd[band], band_psd[band+1], band);
166  fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
167  slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
168  excite[band] = FFMAX(fastleak - lowcomp, slowleak);
169  }
170  begin = 22;
171  } else {
172  /* coupling channel */
173  begin = band_start;
174  fastleak = (s->cpl_fast_leak << 8) + 768;
175  slowleak = (s->cpl_slow_leak << 8) + 768;
176  }
177 
178  for (band = begin; band < band_end; band++) {
179  fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
180  slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
181  excite[band] = FFMAX(fastleak, slowleak);
182  }
183 
184  /* compute masking curve */
185 
186  for (band = band_start; band < band_end; band++) {
187  int tmp = s->db_per_bit - band_psd[band];
188  if (tmp > 0) {
189  excite[band] += tmp >> 2;
190  }
191  mask[band] = FFMAX(ff_ac3_hearing_threshold_tab[band >> s->sr_shift][s->sr_code], excite[band]);
192  }
193 
194  /* delta bit allocation */
195 
196  if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
197  int i, seg, delta;
198  if (dba_nsegs > 8)
199  return -1;
200  band = band_start;
201  for (seg = 0; seg < dba_nsegs; seg++) {
202  band += dba_offsets[seg];
203  if (band >= AC3_CRITICAL_BANDS || dba_lengths[seg] > AC3_CRITICAL_BANDS-band)
204  return -1;
205  if (dba_values[seg] >= 4) {
206  delta = (dba_values[seg] - 3) * 128;
207  } else {
208  delta = (dba_values[seg] - 4) * 128;
209  }
210  for (i = 0; i < dba_lengths[seg]; i++) {
211  mask[band++] += delta;
212  }
213  }
214  }
215  return 0;
216 }
217 
218 /**
219  * Initialize some tables.
220  * note: This function must remain thread safe because it is called by the
221  * AVParser init code.
222  */
224 {
225 #if !CONFIG_HARDCODED_TABLES
226  /* compute ff_ac3_bin_to_band_tab from ff_ac3_band_start_tab */
227  int bin = 0, band;
228  for (band = 0; band < AC3_CRITICAL_BANDS; band++) {
229  int band_end = ff_ac3_band_start_tab[band+1];
230  while (bin < band_end)
231  ff_ac3_bin_to_band_tab[bin++] = band;
232  }
233 #endif /* !CONFIG_HARDCODED_TABLES */
234 }