1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
|
/*
* Common code between AC3 encoder and decoder
* Copyright (c) 2000 Fabrice Bellard.
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file ac3.c
* Common code between AC3 encoder and decoder.
*/
#include "avcodec.h"
#include "ac3.h"
#include "ac3tab.h"
#include "bitstream.h"
static inline int calc_lowcomp1(int a, int b0, int b1, int c)
{
if ((b0 + 256) == b1) {
a = c;
} else if (b0 > b1) {
a = FFMAX(a - 64, 0);
}
return a;
}
static inline int calc_lowcomp(int a, int b0, int b1, int bin)
{
if (bin < 7) {
return calc_lowcomp1(a, b0, b1, 384);
} else if (bin < 20) {
return calc_lowcomp1(a, b0, b1, 320);
} else {
return FFMAX(a - 128, 0);
}
}
void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
int16_t *bndpsd)
{
int bin, i, j, k, end1, v;
/* exponent mapping to PSD */
for(bin=start;bin<end;bin++) {
psd[bin]=(3072 - (exp[bin] << 7));
}
/* PSD integration */
j=start;
k=masktab[start];
do {
v=psd[j];
j++;
end1 = FFMIN(bndtab[k+1], end);
for(i=j;i<end1;i++) {
/* logadd */
int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255);
v = FFMAX(v, psd[j]) + latab[adr];
j++;
}
bndpsd[k]=v;
k++;
} while (end > bndtab[k]);
}
void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
int start, int end, int fgain, int is_lfe,
int deltbae, int deltnseg, uint8_t *deltoffst,
uint8_t *deltlen, uint8_t *deltba,
int16_t *mask)
{
int16_t excite[50]; /* excitation */
int bin, k;
int bndstrt, bndend, begin, end1, tmp;
int lowcomp, fastleak, slowleak;
/* excitation function */
bndstrt = masktab[start];
bndend = masktab[end-1] + 1;
if (bndstrt == 0) {
lowcomp = 0;
lowcomp = calc_lowcomp1(lowcomp, bndpsd[0], bndpsd[1], 384);
excite[0] = bndpsd[0] - fgain - lowcomp;
lowcomp = calc_lowcomp1(lowcomp, bndpsd[1], bndpsd[2], 384);
excite[1] = bndpsd[1] - fgain - lowcomp;
begin = 7;
for (bin = 2; bin < 7; bin++) {
if (!(is_lfe && bin == 6))
lowcomp = calc_lowcomp1(lowcomp, bndpsd[bin], bndpsd[bin+1], 384);
fastleak = bndpsd[bin] - fgain;
slowleak = bndpsd[bin] - s->sgain;
excite[bin] = fastleak - lowcomp;
if (!(is_lfe && bin == 6)) {
if (bndpsd[bin] <= bndpsd[bin+1]) {
begin = bin + 1;
break;
}
}
}
end1=bndend;
if (end1 > 22) end1=22;
for (bin = begin; bin < end1; bin++) {
if (!(is_lfe && bin == 6))
lowcomp = calc_lowcomp(lowcomp, bndpsd[bin], bndpsd[bin+1], bin);
fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain);
slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain);
excite[bin] = FFMAX(fastleak - lowcomp, slowleak);
}
begin = 22;
} else {
/* coupling channel */
begin = bndstrt;
fastleak = (s->cplfleak << 8) + 768;
slowleak = (s->cplsleak << 8) + 768;
}
for (bin = begin; bin < bndend; bin++) {
fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain);
slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain);
excite[bin] = FFMAX(fastleak, slowleak);
}
/* compute masking curve */
for (bin = bndstrt; bin < bndend; bin++) {
tmp = s->dbknee - bndpsd[bin];
if (tmp > 0) {
excite[bin] += tmp >> 2;
}
mask[bin] = FFMAX(hth[bin >> s->halfratecod][s->fscod], excite[bin]);
}
/* delta bit allocation */
if (deltbae == 0 || deltbae == 1) {
int band, seg, delta;
band = 0;
for (seg = 0; seg < deltnseg; seg++) {
band += deltoffst[seg];
if (deltba[seg] >= 4) {
delta = (deltba[seg] - 3) << 7;
} else {
delta = (deltba[seg] - 4) << 7;
}
for (k = 0; k < deltlen[seg]; k++) {
mask[band] += delta;
band++;
}
}
}
}
void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
int snroffset, int floor, uint8_t *bap)
{
int i, j, k, end1, v, address;
/* special case, if snroffset is -960, set all bap's to zero */
if(snroffset == -960) {
memset(bap, 0, 256);
return;
}
i = start;
j = masktab[start];
do {
v = (FFMAX(mask[j] - snroffset - floor, 0) & 0x1FE0) + floor;
end1 = FFMIN(bndtab[j] + bndsz[j], end);
for (k = i; k < end1; k++) {
address = av_clip((psd[i] - v) >> 5, 0, 63);
bap[i] = baptab[address];
i++;
}
} while (end > bndtab[j++]);
}
/* AC3 bit allocation. The algorithm is the one described in the AC3
spec. */
void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
int8_t *exp, int start, int end,
int snroffset, int fgain, int is_lfe,
int deltbae,int deltnseg,
uint8_t *deltoffst, uint8_t *deltlen,
uint8_t *deltba)
{
int16_t psd[256]; /* scaled exponents */
int16_t bndpsd[50]; /* interpolated exponents */
int16_t mask[50]; /* masking value */
ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, bndpsd);
ff_ac3_bit_alloc_calc_mask(s, bndpsd, start, end, fgain, is_lfe,
deltbae, deltnseg, deltoffst, deltlen, deltba,
mask);
ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snroffset, s->floor, bap);
}
/**
* Initializes some tables.
* note: This function must remain thread safe because it is called by the
* AVParser init code.
*/
void ac3_common_init(void)
{
int i, j, k, l, v;
/* compute bndtab and masktab from bandsz */
k = 0;
l = 0;
for(i=0;i<50;i++) {
bndtab[i] = l;
v = bndsz[i];
for(j=0;j<v;j++) masktab[k++]=i;
l += v;
}
bndtab[50] = l;
}
|
