2 * Common code between the AC-3 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 the AC-3 encoder and decoder.
31 #if CONFIG_HARDCODED_TABLES
34 * Starting frequency coefficient bin for each critical band.
36 static const uint8_t band_start_tab[51] = {
37 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
38 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
39 20, 21, 22, 23, 24, 25, 26, 27, 28, 31,
40 34, 37, 40, 43, 46, 49, 55, 61, 67, 73,
41 79, 85, 97, 109, 121, 133, 157, 181, 205, 229, 253
45 * Map each frequency coefficient bin to the critical band that contains it.
47 static const uint8_t bin_to_band_tab[253] = {
49 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
50 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
51 25, 26, 27, 28, 28, 28, 29, 29, 29, 30, 30, 30,
52 31, 31, 31, 32, 32, 32, 33, 33, 33, 34, 34, 34,
53 35, 35, 35, 35, 35, 35, 36, 36, 36, 36, 36, 36,
54 37, 37, 37, 37, 37, 37, 38, 38, 38, 38, 38, 38,
55 39, 39, 39, 39, 39, 39, 40, 40, 40, 40, 40, 40,
56 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
57 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
58 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
59 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44,
60 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
61 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
62 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
63 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
64 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
65 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
66 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
67 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
68 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49,
69 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49
72 #else /* CONFIG_HARDCODED_TABLES */
73 static uint8_t band_start_tab[51];
74 static uint8_t bin_to_band_tab[253];
77 static inline int calc_lowcomp1(int a, int b0, int b1, int c)
79 if ((b0 + 256) == b1) {
87 static inline int calc_lowcomp(int a, int b0, int b1, int bin)
90 return calc_lowcomp1(a, b0, b1, 384);
91 } else if (bin < 20) {
92 return calc_lowcomp1(a, b0, b1, 320);
94 return FFMAX(a - 128, 0);
98 void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
103 /* exponent mapping to PSD */
104 for (bin = start; bin < end; bin++) {
105 psd[bin]=(3072 - (exp[bin] << 7));
108 /* PSD integration */
110 band = bin_to_band_tab[start];
113 int band_end = FFMIN(band_start_tab[band+1], end);
114 for (; bin < band_end; bin++) {
115 int max = FFMAX(v, psd[bin]);
117 int adr = FFMIN(max - ((v + psd[bin] + 1) >> 1), 255);
118 v = max + ff_ac3_log_add_tab[adr];
120 band_psd[band++] = v;
121 } while (end > band_start_tab[band]);
124 int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
125 int start, int end, int fast_gain, int is_lfe,
126 int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
127 uint8_t *dba_lengths, uint8_t *dba_values,
130 int16_t excite[50]; /* excitation */
132 int band_start, band_end, begin, end1;
133 int lowcomp, fastleak, slowleak;
135 /* excitation function */
136 band_start = bin_to_band_tab[start];
137 band_end = bin_to_band_tab[end-1] + 1;
139 if (band_start == 0) {
141 lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384);
142 excite[0] = band_psd[0] - fast_gain - lowcomp;
143 lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384);
144 excite[1] = band_psd[1] - fast_gain - lowcomp;
146 for (band = 2; band < 7; band++) {
147 if (!(is_lfe && band == 6))
148 lowcomp = calc_lowcomp1(lowcomp, band_psd[band], band_psd[band+1], 384);
149 fastleak = band_psd[band] - fast_gain;
150 slowleak = band_psd[band] - s->slow_gain;
151 excite[band] = fastleak - lowcomp;
152 if (!(is_lfe && band == 6)) {
153 if (band_psd[band] <= band_psd[band+1]) {
160 end1 = FFMIN(band_end, 22);
161 for (band = begin; band < end1; band++) {
162 if (!(is_lfe && band == 6))
163 lowcomp = calc_lowcomp(lowcomp, band_psd[band], band_psd[band+1], band);
164 fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
165 slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
166 excite[band] = FFMAX(fastleak - lowcomp, slowleak);
170 /* coupling channel */
172 fastleak = (s->cpl_fast_leak << 8) + 768;
173 slowleak = (s->cpl_slow_leak << 8) + 768;
176 for (band = begin; band < band_end; band++) {
177 fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
178 slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
179 excite[band] = FFMAX(fastleak, slowleak);
182 /* compute masking curve */
184 for (band = band_start; band < band_end; band++) {
185 int tmp = s->db_per_bit - band_psd[band];
187 excite[band] += tmp >> 2;
189 mask[band] = FFMAX(ff_ac3_hearing_threshold_tab[band >> s->sr_shift][s->sr_code], excite[band]);
192 /* delta bit allocation */
194 if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
199 for (seg = 0; seg < dba_nsegs; seg++) {
200 band += dba_offsets[seg];
201 if (band >= 50 || dba_lengths[seg] > 50-band)
203 if (dba_values[seg] >= 4) {
204 delta = (dba_values[seg] - 3) << 7;
206 delta = (dba_values[seg] - 4) << 7;
208 for (i = 0; i < dba_lengths[seg]; i++) {
209 mask[band++] += delta;
216 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
217 int snr_offset, int floor,
218 const uint8_t *bap_tab, uint8_t *bap)
222 /* special case, if snr offset is -960, set all bap's to zero */
223 if (snr_offset == -960) {
229 band = bin_to_band_tab[start];
231 int m = (FFMAX(mask[band] - snr_offset - floor, 0) & 0x1FE0) + floor;
232 int band_end = FFMIN(band_start_tab[band+1], end);
233 for (; bin < band_end; bin++) {
234 int address = av_clip((psd[bin] - m) >> 5, 0, 63);
235 bap[bin] = bap_tab[address];
237 } while (end > band_start_tab[band++]);
240 /* AC-3 bit allocation. The algorithm is the one described in the AC-3
242 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
243 int8_t *exp, int start, int end,
244 int snr_offset, int fast_gain, int is_lfe,
245 int dba_mode, int dba_nsegs,
246 uint8_t *dba_offsets, uint8_t *dba_lengths,
249 int16_t psd[256]; /* scaled exponents */
250 int16_t band_psd[50]; /* interpolated exponents */
251 int16_t mask[50]; /* masking value */
253 ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd);
255 ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe,
256 dba_mode, dba_nsegs, dba_offsets, dba_lengths,
259 ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor,
260 ff_ac3_bap_tab, bap);
264 * Initialize some tables.
265 * note: This function must remain thread safe because it is called by the
266 * AVParser init code.
268 av_cold void ac3_common_init(void)
270 #if !CONFIG_HARDCODED_TABLES
271 /* compute bndtab and masktab from bandsz */
273 for (band = 0; band < 50; band++) {
274 int band_end = bin + ff_ac3_critical_band_size_tab[band];
275 band_start_tab[band] = bin;
276 while (bin < band_end)
277 bin_to_band_tab[bin++] = band;
279 band_start_tab[50] = bin;
280 #endif /* !CONFIG_HARDCODED_TABLES */