FFmpeg
ac3.c
Go to the documentation of this file.
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 "ac3.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 /**
43  * Map each frequency coefficient bin to the critical band that contains it.
44  */
45 const uint8_t ff_ac3_bin_to_band_tab[253] = {
46  0,
47  1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
48  13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
49  25, 26, 27, 28, 28, 28, 29, 29, 29, 30, 30, 30,
50  31, 31, 31, 32, 32, 32, 33, 33, 33, 34, 34, 34,
51  35, 35, 35, 35, 35, 35, 36, 36, 36, 36, 36, 36,
52  37, 37, 37, 37, 37, 37, 38, 38, 38, 38, 38, 38,
53  39, 39, 39, 39, 39, 39, 40, 40, 40, 40, 40, 40,
54  41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
55  42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
56  43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
57  44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44,
58  45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
59  45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
60  46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
61  46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
62  47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
63  47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
64  48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
65  48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
66  49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49,
67  49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49
68 };
69 
70 static inline int calc_lowcomp1(int a, int b0, int b1, int c)
71 {
72  if ((b0 + 256) == b1) {
73  a = c;
74  } else if (b0 > b1) {
75  a = FFMAX(a - 64, 0);
76  }
77  return a;
78 }
79 
80 static inline int calc_lowcomp(int a, int b0, int b1, int bin)
81 {
82  if (bin < 7) {
83  return calc_lowcomp1(a, b0, b1, 384);
84  } else if (bin < 20) {
85  return calc_lowcomp1(a, b0, b1, 320);
86  } else {
87  return FFMAX(a - 128, 0);
88  }
89 }
90 
91 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
92  int16_t *band_psd)
93 {
94  int bin, band;
95 
96  /* exponent mapping to PSD */
97  for (bin = start; bin < end; bin++) {
98  psd[bin]=(3072 - (exp[bin] << 7));
99  }
100 
101  /* PSD integration */
102  bin = start;
103  band = ff_ac3_bin_to_band_tab[start];
104  do {
105  int v = psd[bin++];
106  int band_end = FFMIN(ff_ac3_band_start_tab[band+1], end);
107  for (; bin < band_end; bin++) {
108  int max = FFMAX(v, psd[bin]);
109  /* logadd */
110  int adr = FFMIN(max - ((v + psd[bin] + 1) >> 1), 255);
111  v = max + ff_ac3_log_add_tab[adr];
112  }
113  band_psd[band++] = v;
114  } while (end > ff_ac3_band_start_tab[band]);
115 }
116 
117 int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
118  int start, int end, int fast_gain, int is_lfe,
119  int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
120  uint8_t *dba_lengths, uint8_t *dba_values,
121  int16_t *mask)
122 {
123  int16_t excite[AC3_CRITICAL_BANDS]; /* excitation */
124  int band;
125  int band_start, band_end, begin, end1;
126  int lowcomp, fastleak, slowleak;
127 
128  if (end <= 0)
129  return AVERROR_INVALIDDATA;
130 
131  /* excitation function */
132  band_start = ff_ac3_bin_to_band_tab[start];
133  band_end = ff_ac3_bin_to_band_tab[end-1] + 1;
134 
135  if (band_start == 0) {
136  lowcomp = 0;
137  lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384);
138  excite[0] = band_psd[0] - fast_gain - lowcomp;
139  lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384);
140  excite[1] = band_psd[1] - fast_gain - lowcomp;
141  begin = 7;
142  for (band = 2; band < 7; band++) {
143  if (!(is_lfe && band == 6))
144  lowcomp = calc_lowcomp1(lowcomp, band_psd[band], band_psd[band+1], 384);
145  fastleak = band_psd[band] - fast_gain;
146  slowleak = band_psd[band] - s->slow_gain;
147  excite[band] = fastleak - lowcomp;
148  if (!(is_lfe && band == 6)) {
149  if (band_psd[band] <= band_psd[band+1]) {
150  begin = band + 1;
151  break;
152  }
153  }
154  }
155 
156  end1 = FFMIN(band_end, 22);
157  for (band = begin; band < end1; band++) {
158  if (!(is_lfe && band == 6))
159  lowcomp = calc_lowcomp(lowcomp, band_psd[band], band_psd[band+1], band);
160  fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
161  slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
162  excite[band] = FFMAX(fastleak - lowcomp, slowleak);
163  }
164  begin = 22;
165  } else {
166  /* coupling channel */
167  begin = band_start;
168  fastleak = (s->cpl_fast_leak << 8) + 768;
169  slowleak = (s->cpl_slow_leak << 8) + 768;
170  }
171 
172  for (band = begin; band < band_end; band++) {
173  fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
174  slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
175  excite[band] = FFMAX(fastleak, slowleak);
176  }
177 
178  /* compute masking curve */
179 
180  for (band = band_start; band < band_end; band++) {
181  int tmp = s->db_per_bit - band_psd[band];
182  if (tmp > 0) {
183  excite[band] += tmp >> 2;
184  }
185  mask[band] = FFMAX(ff_ac3_hearing_threshold_tab[band >> s->sr_shift][s->sr_code], excite[band]);
186  }
187 
188  /* delta bit allocation */
189 
190  if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
191  int i, seg, delta;
192  if (dba_nsegs > 8)
193  return -1;
194  band = band_start;
195  for (seg = 0; seg < dba_nsegs; seg++) {
196  band += dba_offsets[seg];
197  if (band >= AC3_CRITICAL_BANDS || dba_lengths[seg] > AC3_CRITICAL_BANDS-band)
198  return -1;
199  if (dba_values[seg] >= 4) {
200  delta = (dba_values[seg] - 3) * 128;
201  } else {
202  delta = (dba_values[seg] - 4) * 128;
203  }
204  for (i = 0; i < dba_lengths[seg]; i++) {
205  mask[band++] += delta;
206  }
207  }
208  }
209  return 0;
210 }
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:45
calc_lowcomp
static int calc_lowcomp(int a, int b0, int b1, int bin)
Definition: ac3.c:80
tmp
static uint8_t tmp[11]
Definition: aes_ctr.c:26
AC3_CRITICAL_BANDS
#define AC3_CRITICAL_BANDS
Definition: ac3.h:42
max
#define max(a, b)
Definition: cuda_runtime.h:33
FFMAX
#define FFMAX(a, b)
Definition: macros.h:47
b1
static double b1(void *priv, double x, double y)
Definition: vf_xfade.c:1703
ff_ac3_log_add_tab
const uint8_t ff_ac3_log_add_tab[260]
Definition: ac3tab.c:117
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:34
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:70
ff_ac3_hearing_threshold_tab
const uint16_t ff_ac3_hearing_threshold_tab[AC3_CRITICAL_BANDS][3]
Definition: ac3tab.c:146
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
#define i(width, name, range_min, range_max)
Definition: cbs_h2645.c:271
common.h
delta
float delta
Definition: vorbis_enc_data.h:430
FFMIN
#define FFMIN(a, b)
Definition: macros.h:49
DBA_NEW
@ DBA_NEW
Definition: ac3.h:117
AC3BitAllocParameters
Definition: ac3.h:166
DBA_REUSE
@ DBA_REUSE
Definition: ac3.h:116
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:117
ac3.h
AVERROR_INVALIDDATA
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:61
b0
static double b0(void *priv, double x, double y)
Definition: vf_xfade.c:1702
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:91
Generated on Wed Aug 24 2022 21:37:24 for FFmpeg by   doxygen 1.8.17