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
23 * @file libavcodec/ac3.c
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 * Maps 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
++) {
116 int adr
= FFMIN(FFABS(v
- psd
[bin
]) >> 1, 255);
117 v
= FFMAX(v
, psd
[bin
]) + ff_ac3_log_add_tab
[adr
];
119 band_psd
[band
++] = v
;
120 } while (end
> band_start_tab
[band
]);
123 int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters
*s
, int16_t *band_psd
,
124 int start
, int end
, int fast_gain
, int is_lfe
,
125 int dba_mode
, int dba_nsegs
, uint8_t *dba_offsets
,
126 uint8_t *dba_lengths
, uint8_t *dba_values
,
129 int16_t excite
[50]; /* excitation */
131 int band_start
, band_end
, begin
, end1
;
132 int lowcomp
, fastleak
, slowleak
;
134 /* excitation function */
135 band_start
= bin_to_band_tab
[start
];
136 band_end
= bin_to_band_tab
[end
-1] + 1;
138 if (band_start
== 0) {
140 lowcomp
= calc_lowcomp1(lowcomp
, band_psd
[0], band_psd
[1], 384);
141 excite
[0] = band_psd
[0] - fast_gain
- lowcomp
;
142 lowcomp
= calc_lowcomp1(lowcomp
, band_psd
[1], band_psd
[2], 384);
143 excite
[1] = band_psd
[1] - fast_gain
- lowcomp
;
145 for (band
= 2; band
< 7; band
++) {
146 if (!(is_lfe
&& band
== 6))
147 lowcomp
= calc_lowcomp1(lowcomp
, band_psd
[band
], band_psd
[band
+1], 384);
148 fastleak
= band_psd
[band
] - fast_gain
;
149 slowleak
= band_psd
[band
] - s
->slow_gain
;
150 excite
[band
] = fastleak
- lowcomp
;
151 if (!(is_lfe
&& band
== 6)) {
152 if (band_psd
[band
] <= band_psd
[band
+1]) {
159 end1
= FFMIN(band_end
, 22);
160 for (band
= begin
; band
< end1
; band
++) {
161 if (!(is_lfe
&& band
== 6))
162 lowcomp
= calc_lowcomp(lowcomp
, band_psd
[band
], band_psd
[band
+1], band
);
163 fastleak
= FFMAX(fastleak
- s
->fast_decay
, band_psd
[band
] - fast_gain
);
164 slowleak
= FFMAX(slowleak
- s
->slow_decay
, band_psd
[band
] - s
->slow_gain
);
165 excite
[band
] = FFMAX(fastleak
- lowcomp
, slowleak
);
169 /* coupling channel */
171 fastleak
= (s
->cpl_fast_leak
<< 8) + 768;
172 slowleak
= (s
->cpl_slow_leak
<< 8) + 768;
175 for (band
= begin
; band
< band_end
; band
++) {
176 fastleak
= FFMAX(fastleak
- s
->fast_decay
, band_psd
[band
] - fast_gain
);
177 slowleak
= FFMAX(slowleak
- s
->slow_decay
, band_psd
[band
] - s
->slow_gain
);
178 excite
[band
] = FFMAX(fastleak
, slowleak
);
181 /* compute masking curve */
183 for (band
= band_start
; band
< band_end
; band
++) {
184 int tmp
= s
->db_per_bit
- band_psd
[band
];
186 excite
[band
] += tmp
>> 2;
188 mask
[band
] = FFMAX(ff_ac3_hearing_threshold_tab
[band
>> s
->sr_shift
][s
->sr_code
], excite
[band
]);
191 /* delta bit allocation */
193 if (dba_mode
== DBA_REUSE
|| dba_mode
== DBA_NEW
) {
198 for (seg
= 0; seg
< dba_nsegs
; seg
++) {
199 band
+= dba_offsets
[seg
];
200 if (band
>= 50 || dba_lengths
[seg
] > 50-band
)
202 if (dba_values
[seg
] >= 4) {
203 delta
= (dba_values
[seg
] - 3) << 7;
205 delta
= (dba_values
[seg
] - 4) << 7;
207 for (i
= 0; i
< dba_lengths
[seg
]; i
++) {
208 mask
[band
++] += delta
;
215 void ff_ac3_bit_alloc_calc_bap(int16_t *mask
, int16_t *psd
, int start
, int end
,
216 int snr_offset
, int floor
,
217 const uint8_t *bap_tab
, uint8_t *bap
)
219 int i
, j
, k
, end1
, v
, address
;
221 /* special case, if snr offset is -960, set all bap's to zero */
222 if (snr_offset
== -960) {
228 j
= bin_to_band_tab
[start
];
230 v
= (FFMAX(mask
[j
] - snr_offset
- floor
, 0) & 0x1FE0) + floor
;
231 end1
= FFMIN(band_start_tab
[j
] + ff_ac3_critical_band_size_tab
[j
], end
);
232 for (k
= i
; k
< end1
; k
++) {
233 address
= av_clip((psd
[i
] - v
) >> 5, 0, 63);
234 bap
[i
] = bap_tab
[address
];
237 } while (end
> band_start_tab
[j
++]);
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 * Initializes 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 */