FFmpeg
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  */
46 const uint8_t ff_ac3_bin_to_band_tab[253] = {
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;
104  band = ff_ac3_bin_to_band_tab[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 }
ff_ac3_bin_to_band_tab
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
calc_lowcomp
static int calc_lowcomp(int a, int b0, int b1, int bin)
Definition: ac3.c:81
tmp
static uint8_t tmp[11]
Definition: aes_ctr.c:27
AC3_CRITICAL_BANDS
#define AC3_CRITICAL_BANDS
Definition: ac3.h:39
max
#define max(a, b)
Definition: cuda_runtime.h:33
b1
static double b1(void *priv, double x, double y)
Definition: vf_xfade.c:1665
ff_ac3_log_add_tab
const uint8_t ff_ac3_log_add_tab[260]
Definition: ac3tab.c:132
mask
static const uint16_t mask[17]
Definition: lzw.c:38
s
#define s(width, name)
Definition: cbs_vp9.c:257
ff_ac3_band_start_tab
const uint8_t ff_ac3_band_start_tab[AC3_CRITICAL_BANDS+1]
Starting frequency coefficient bin for each critical band.
Definition: ac3.c:35
exp
int8_t exp
Definition: eval.c:72
c
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
calc_lowcomp1
static int calc_lowcomp1(int a, int b0, int b1, int c)
Definition: ac3.c:71
FFMAX
#define FFMAX(a, b)
Definition: common.h:103
ff_ac3_hearing_threshold_tab
const uint16_t ff_ac3_hearing_threshold_tab[AC3_CRITICAL_BANDS][3]
Definition: ac3tab.c:161
FFMIN
#define FFMIN(a, b)
Definition: common.h:105
a
The reader does not expect b to be semantically here and if the code is changed by maybe adding a a division or other the signedness will almost certainly be mistaken To avoid this confusion a new type was SUINT is the C unsigned type but it holds a signed int to use the same example SUINT a
Definition: undefined.txt:41
i
int i
Definition: input.c:407
common.h
delta
float delta
Definition: vorbis_enc_data.h:457
DBA_NEW
@ DBA_NEW
Definition: ac3.h:116
avcodec.h
AC3BitAllocParameters
Definition: ac3.h:165
DBA_REUSE
@ DBA_REUSE
Definition: ac3.h:115
ff_ac3_bit_alloc_calc_mask
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
ac3.h
AVERROR_INVALIDDATA
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:59
b0
static double b0(void *priv, double x, double y)
Definition: vf_xfade.c:1664
ff_ac3_bit_alloc_calc_psd
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