2 * Common code between AC3 encoder and decoder
3 * Copyright (c) 2000 Fabrice Bellard.
5 * This file is part of FFmpeg.
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.
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.
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
24 * Common code between AC3 encoder and decoder.
29 #include "bitstream.h"
31 static uint8_t bndtab[51];
32 static uint8_t masktab[253];
34 static inline int calc_lowcomp1(int a, int b0, int b1, int c)
36 if ((b0 + 256) == b1) {
44 static inline int calc_lowcomp(int a, int b0, int b1, int bin)
47 return calc_lowcomp1(a, b0, b1, 384);
48 } else if (bin < 20) {
49 return calc_lowcomp1(a, b0, b1, 320);
51 return FFMAX(a - 128, 0);
55 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
58 int bin, i, j, k, end1, v;
60 /* exponent mapping to PSD */
61 for(bin=start;bin<end;bin++) {
62 psd[bin]=(3072 - (exp[bin] << 7));
71 end1 = FFMIN(bndtab[k+1], end);
74 int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255);
75 v = FFMAX(v, psd[j]) + ff_ac3_latab[adr];
80 } while (end > bndtab[k]);
83 void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
84 int start, int end, int fgain, int is_lfe,
85 int deltbae, int deltnseg, uint8_t *deltoffst,
86 uint8_t *deltlen, uint8_t *deltba,
89 int16_t excite[50]; /* excitation */
91 int bndstrt, bndend, begin, end1, tmp;
92 int lowcomp, fastleak, slowleak;
94 /* excitation function */
95 bndstrt = masktab[start];
96 bndend = masktab[end-1] + 1;
100 lowcomp = calc_lowcomp1(lowcomp, bndpsd[0], bndpsd[1], 384);
101 excite[0] = bndpsd[0] - fgain - lowcomp;
102 lowcomp = calc_lowcomp1(lowcomp, bndpsd[1], bndpsd[2], 384);
103 excite[1] = bndpsd[1] - fgain - lowcomp;
105 for (bin = 2; bin < 7; bin++) {
106 if (!(is_lfe && bin == 6))
107 lowcomp = calc_lowcomp1(lowcomp, bndpsd[bin], bndpsd[bin+1], 384);
108 fastleak = bndpsd[bin] - fgain;
109 slowleak = bndpsd[bin] - s->sgain;
110 excite[bin] = fastleak - lowcomp;
111 if (!(is_lfe && bin == 6)) {
112 if (bndpsd[bin] <= bndpsd[bin+1]) {
120 if (end1 > 22) end1=22;
122 for (bin = begin; bin < end1; bin++) {
123 if (!(is_lfe && bin == 6))
124 lowcomp = calc_lowcomp(lowcomp, bndpsd[bin], bndpsd[bin+1], bin);
126 fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain);
127 slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain);
128 excite[bin] = FFMAX(fastleak - lowcomp, slowleak);
132 /* coupling channel */
135 fastleak = (s->cplfleak << 8) + 768;
136 slowleak = (s->cplsleak << 8) + 768;
139 for (bin = begin; bin < bndend; bin++) {
140 fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain);
141 slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain);
142 excite[bin] = FFMAX(fastleak, slowleak);
145 /* compute masking curve */
147 for (bin = bndstrt; bin < bndend; bin++) {
148 tmp = s->dbknee - bndpsd[bin];
150 excite[bin] += tmp >> 2;
152 mask[bin] = FFMAX(ff_ac3_hth[bin >> s->halfratecod][s->fscod], excite[bin]);
155 /* delta bit allocation */
157 if (deltbae == DBA_REUSE || deltbae == DBA_NEW) {
158 int band, seg, delta;
160 for (seg = 0; seg < deltnseg; seg++) {
161 band += deltoffst[seg];
162 if (deltba[seg] >= 4) {
163 delta = (deltba[seg] - 3) << 7;
165 delta = (deltba[seg] - 4) << 7;
167 for (k = 0; k < deltlen[seg]; k++) {
175 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
176 int snroffset, int floor, uint8_t *bap)
178 int i, j, k, end1, v, address;
180 /* special case, if snroffset is -960, set all bap's to zero */
181 if(snroffset == -960) {
189 v = (FFMAX(mask[j] - snroffset - floor, 0) & 0x1FE0) + floor;
190 end1 = FFMIN(bndtab[j] + ff_ac3_bndsz[j], end);
191 for (k = i; k < end1; k++) {
192 address = av_clip((psd[i] - v) >> 5, 0, 63);
193 bap[i] = ff_ac3_baptab[address];
196 } while (end > bndtab[j++]);
199 /* AC3 bit allocation. The algorithm is the one described in the AC3
201 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
202 int8_t *exp, int start, int end,
203 int snroffset, int fgain, int is_lfe,
204 int deltbae,int deltnseg,
205 uint8_t *deltoffst, uint8_t *deltlen,
208 int16_t psd[256]; /* scaled exponents */
209 int16_t bndpsd[50]; /* interpolated exponents */
210 int16_t mask[50]; /* masking value */
212 ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, bndpsd);
214 ff_ac3_bit_alloc_calc_mask(s, bndpsd, start, end, fgain, is_lfe,
215 deltbae, deltnseg, deltoffst, deltlen, deltba,
218 ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snroffset, s->floor, bap);
222 * Initializes some tables.
223 * note: This function must remain thread safe because it is called by the
224 * AVParser init code.
226 void ac3_common_init(void)
229 /* compute bndtab and masktab from bandsz */
235 for(j=0;j<v;j++) masktab[k++]=i;