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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 "libavutil/common.h"
28 
29 #include "avcodec.h"
30 #include "ac3.h"
31 
32 /**
33  * Starting frequency coefficient bin for each critical band.
34  */
36  0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
37  10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
38  20, 21, 22, 23, 24, 25, 26, 27, 28, 31,
39  34, 37, 40, 43, 46, 49, 55, 61, 67, 73,
40  79, 85, 97, 109, 121, 133, 157, 181, 205, 229, 253
41 };
42 
43 /**
44  * Map each frequency coefficient bin to the critical band that contains it.
45  */
47  0,
48  1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
49  13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
50  25, 26, 27, 28, 28, 28, 29, 29, 29, 30, 30, 30,
51  31, 31, 31, 32, 32, 32, 33, 33, 33, 34, 34, 34,
52  35, 35, 35, 35, 35, 35, 36, 36, 36, 36, 36, 36,
53  37, 37, 37, 37, 37, 37, 38, 38, 38, 38, 38, 38,
54  39, 39, 39, 39, 39, 39, 40, 40, 40, 40, 40, 40,
55  41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
56  42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
57  43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
58  44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44,
59  45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
60  45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
61  46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
62  46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
63  47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
64  47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
65  48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
66  48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
67  49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49,
68  49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49
69 };
70 
71 static inline int calc_lowcomp1(int a, int b0, int b1, int c)
72 {
73  if ((b0 + 256) == b1) {
74  a = c;
75  } else if (b0 > b1) {
76  a = FFMAX(a - 64, 0);
77  }
78  return a;
79 }
80 
81 static inline int calc_lowcomp(int a, int b0, int b1, int bin)
82 {
83  if (bin < 7) {
84  return calc_lowcomp1(a, b0, b1, 384);
85  } else if (bin < 20) {
86  return calc_lowcomp1(a, b0, b1, 320);
87  } else {
88  return FFMAX(a - 128, 0);
89  }
90 }
91 
92 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
93  int16_t *band_psd)
94 {
95  int bin, band;
96 
97  /* exponent mapping to PSD */
98  for (bin = start; bin < end; bin++) {
99  psd[bin]=(3072 - (exp[bin] << 7));
100  }
101 
102  /* PSD integration */
103  bin = start;
105  do {
106  int v = psd[bin++];
107  int band_end = FFMIN(ff_ac3_band_start_tab[band+1], end);
108  for (; bin < band_end; bin++) {
109  int max = FFMAX(v, psd[bin]);
110  /* logadd */
111  int adr = FFMIN(max - ((v + psd[bin] + 1) >> 1), 255);
112  v = max + ff_ac3_log_add_tab[adr];
113  }
114  band_psd[band++] = v;
115  } while (end > ff_ac3_band_start_tab[band]);
116 }
117 
119  int start, int end, int fast_gain, int is_lfe,
120  int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
121  uint8_t *dba_lengths, uint8_t *dba_values,
122  int16_t *mask)
123 {
124  int16_t excite[AC3_CRITICAL_BANDS]; /* excitation */
125  int band;
126  int band_start, band_end, begin, end1;
127  int lowcomp, fastleak, slowleak;
128 
129  if (end <= 0)
130  return AVERROR_INVALIDDATA;
131 
132  /* excitation function */
133  band_start = ff_ac3_bin_to_band_tab[start];
134  band_end = ff_ac3_bin_to_band_tab[end-1] + 1;
135 
136  if (band_start == 0) {
137  lowcomp = 0;
138  lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384);
139  excite[0] = band_psd[0] - fast_gain - lowcomp;
140  lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384);
141  excite[1] = band_psd[1] - fast_gain - lowcomp;
142  begin = 7;
143  for (band = 2; band < 7; band++) {
144  if (!(is_lfe && band == 6))
145  lowcomp = calc_lowcomp1(lowcomp, band_psd[band], band_psd[band+1], 384);
146  fastleak = band_psd[band] - fast_gain;
147  slowleak = band_psd[band] - s->slow_gain;
148  excite[band] = fastleak - lowcomp;
149  if (!(is_lfe && band == 6)) {
150  if (band_psd[band] <= band_psd[band+1]) {
151  begin = band + 1;
152  break;
153  }
154  }
155  }
156 
157  end1 = FFMIN(band_end, 22);
158  for (band = begin; band < end1; band++) {
159  if (!(is_lfe && band == 6))
160  lowcomp = calc_lowcomp(lowcomp, band_psd[band], band_psd[band+1], band);
161  fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
162  slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
163  excite[band] = FFMAX(fastleak - lowcomp, slowleak);
164  }
165  begin = 22;
166  } else {
167  /* coupling channel */
168  begin = band_start;
169  fastleak = (s->cpl_fast_leak << 8) + 768;
170  slowleak = (s->cpl_slow_leak << 8) + 768;
171  }
172 
173  for (band = begin; band < band_end; band++) {
174  fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
175  slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
176  excite[band] = FFMAX(fastleak, slowleak);
177  }
178 
179  /* compute masking curve */
180 
181  for (band = band_start; band < band_end; band++) {
182  int tmp = s->db_per_bit - band_psd[band];
183  if (tmp > 0) {
184  excite[band] += tmp >> 2;
185  }
186  mask[band] = FFMAX(ff_ac3_hearing_threshold_tab[band >> s->sr_shift][s->sr_code], excite[band]);
187  }
188 
189  /* delta bit allocation */
190 
191  if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
192  int i, seg, delta;
193  if (dba_nsegs > 8)
194  return -1;
195  band = band_start;
196  for (seg = 0; seg < dba_nsegs; seg++) {
197  band += dba_offsets[seg];
198  if (band >= AC3_CRITICAL_BANDS || dba_lengths[seg] > AC3_CRITICAL_BANDS-band)
199  return -1;
200  if (dba_values[seg] >= 4) {
201  delta = (dba_values[seg] - 3) * 128;
202  } else {
203  delta = (dba_values[seg] - 4) * 128;
204  }
205  for (i = 0; i < dba_lengths[seg]; i++) {
206  mask[band++] += delta;
207  }
208  }
209  }
210  return 0;
211 }
const char * s
Definition: avisynth_c.h:631
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:59
Definition: ac3.h:115
const uint8_t ff_ac3_bin_to_band_tab[253]
Map each frequency coefficient bin to the critical band that contains it.
Definition: ac3.c:46
uint8_t
float delta
const uint16_t ff_ac3_hearing_threshold_tab[AC3_CRITICAL_BANDS][3]
Definition: ac3tab.c:217
static av_cold int end(AVCodecContext *avctx)
Definition: avrndec.c:90
static const uint16_t mask[17]
Definition: lzw.c:38
int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd, int start, int end, int fast_gain, int is_lfe, int dba_mode, int dba_nsegs, uint8_t *dba_offsets, uint8_t *dba_lengths, uint8_t *dba_values, int16_t *mask)
Calculate the masking curve.
Definition: ac3.c:118
const uint8_t ff_ac3_band_start_tab[AC3_CRITICAL_BANDS+1]
Starting frequency coefficient bin for each critical band.
Definition: ac3.c:35
Definition: ac3.h:116
#define FFMAX(a, b)
Definition: common.h:94
int8_t exp
Definition: eval.c:64
static int calc_lowcomp(int a, int b0, int b1, int bin)
Definition: ac3.c:81
#define FFMIN(a, b)
Definition: common.h:96
static int calc_lowcomp1(int a, int b0, int b1, int c)
Definition: ac3.c:71
Libavcodec external API header.
const uint8_t ff_ac3_log_add_tab[260]
Definition: ac3tab.c:188
#define AC3_CRITICAL_BANDS
Definition: ac3.h:39
common internal and external API header
static double c[64]
void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd, int16_t *band_psd)
Calculate the log power-spectral density of the input signal.
Definition: ac3.c:92
static uint8_t tmp[8]
Definition: des.c:38
void INT64 start
Definition: avisynth_c.h:553
Common code between the AC-3 encoder and decoder.