Libav
ac3enc_fixed.c
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1 /*
2  * The simplest AC-3 encoder
3  * Copyright (c) 2000 Fabrice Bellard
4  * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
5  * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
6  *
7  * This file is part of Libav.
8  *
9  * Libav is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU Lesser General Public
11  * License as published by the Free Software Foundation; either
12  * version 2.1 of the License, or (at your option) any later version.
13  *
14  * Libav is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17  * Lesser General Public License for more details.
18  *
19  * You should have received a copy of the GNU Lesser General Public
20  * License along with Libav; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22  */
23 
29 #define FFT_FLOAT 0
30 #undef CONFIG_AC3ENC_FLOAT
31 #include "internal.h"
32 #include "ac3enc.h"
33 #include "eac3enc.h"
34 
35 #define AC3ENC_TYPE AC3ENC_TYPE_AC3_FIXED
36 #include "ac3enc_opts_template.c"
37 static const AVClass ac3enc_class = { "Fixed-Point AC-3 Encoder", av_default_item_name,
39 
40 #include "ac3enc_template.c"
41 
42 
49 {
50  ff_mdct_end(&s->mdct);
51 }
52 
53 
61 {
62  int ret = ff_mdct_init(&s->mdct, 9, 0, -1.0);
63  s->mdct_window = ff_ac3_window;
64  return ret;
65 }
66 
67 
68 /*
69  * Normalize the input samples to use the maximum available precision.
70  * This assumes signed 16-bit input samples.
71  */
73 {
75  v = 14 - av_log2(v);
76  if (v > 0)
78  /* +6 to right-shift from 31-bit to 25-bit */
79  return v + 6;
80 }
81 
82 
83 /*
84  * Scale MDCT coefficients to 25-bit signed fixed-point.
85  */
87 {
88  int blk, ch;
89 
90  for (blk = 0; blk < s->num_blocks; blk++) {
91  AC3Block *block = &s->blocks[blk];
92  for (ch = 1; ch <= s->channels; ch++) {
94  block->coeff_shift[ch]);
95  }
96  }
97 }
98 
99 
100 /*
101  * Clip MDCT coefficients to allowable range.
102  */
103 static void clip_coefficients(DSPContext *dsp, int32_t *coef, unsigned int len)
104 {
105  dsp->vector_clip_int32(coef, coef, COEF_MIN, COEF_MAX, len);
106 }
107 
108 
109 /*
110  * Calculate a single coupling coordinate.
111  */
112 static CoefType calc_cpl_coord(CoefSumType energy_ch, CoefSumType energy_cpl)
113 {
114  if (energy_cpl <= COEF_MAX) {
115  return 1048576;
116  } else {
117  uint64_t coord = energy_ch / (energy_cpl >> 24);
118  uint32_t coord32 = FFMIN(coord, 1073741824);
119  coord32 = ff_sqrt(coord32) << 9;
120  return FFMIN(coord32, COEF_MAX);
121  }
122 }
123 
124 
126 {
127  AC3EncodeContext *s = avctx->priv_data;
128  s->fixed_point = 1;
129  return ff_ac3_encode_init(avctx);
130 }
131 
132 
134  .name = "ac3_fixed",
135  .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
136  .type = AVMEDIA_TYPE_AUDIO,
137  .id = AV_CODEC_ID_AC3,
138  .priv_data_size = sizeof(AC3EncodeContext),
140  .encode2 = ff_ac3_fixed_encode_frame,
142  .sample_fmts = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_S16P,
144  .priv_class = &ac3enc_class,
145  .channel_layouts = ff_ac3_channel_layouts,
146  .defaults = ac3_defaults,
147 };