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 CONFIG_FFT_FLOAT 0
30 #undef CONFIG_AC3ENC_FLOAT
31 #include "ac3enc.h"
32 #include "eac3enc.h"
33 
34 #define AC3ENC_TYPE AC3ENC_TYPE_AC3_FIXED
35 #include "ac3enc_opts_template.c"
36 static const AVClass ac3enc_class = { "Fixed-Point AC-3 Encoder", av_default_item_name,
38 
39 #include "ac3enc_template.c"
40 
41 
48 {
49  ff_mdct_end(&s->mdct);
50 }
51 
52 
60 {
61  int ret = ff_mdct_init(&s->mdct, 9, 0, -1.0);
62  s->mdct_window = ff_ac3_window;
63  return ret;
64 }
65 
66 
67 /*
68  * Apply KBD window to input samples prior to MDCT.
69  */
70 static void apply_window(DSPContext *dsp, int16_t *output, const int16_t *input,
71  const int16_t *window, unsigned int len)
72 {
73  dsp->apply_window_int16(output, input, window, len);
74 }
75 
76 
77 /*
78  * Normalize the input samples to use the maximum available precision.
79  * This assumes signed 16-bit input samples.
80  */
82 {
84  v = 14 - av_log2(v);
85  if (v > 0)
87  /* +6 to right-shift from 31-bit to 25-bit */
88  return v + 6;
89 }
90 
91 
92 /*
93  * Scale MDCT coefficients to 25-bit signed fixed-point.
94  */
96 {
97  int blk, ch;
98 
99  for (blk = 0; blk < s->num_blocks; blk++) {
100  AC3Block *block = &s->blocks[blk];
101  for (ch = 1; ch <= s->channels; ch++) {
103  block->coeff_shift[ch]);
104  }
105  }
106 }
107 
108 
109 /*
110  * Clip MDCT coefficients to allowable range.
111  */
112 static void clip_coefficients(DSPContext *dsp, int32_t *coef, unsigned int len)
113 {
114  dsp->vector_clip_int32(coef, coef, COEF_MIN, COEF_MAX, len);
115 }
116 
117 
118 /*
119  * Calculate a single coupling coordinate.
120  */
121 static CoefType calc_cpl_coord(CoefSumType energy_ch, CoefSumType energy_cpl)
122 {
123  if (energy_cpl <= COEF_MAX) {
124  return 1048576;
125  } else {
126  uint64_t coord = energy_ch / (energy_cpl >> 24);
127  uint32_t coord32 = FFMIN(coord, 1073741824);
128  coord32 = ff_sqrt(coord32) << 9;
129  return FFMIN(coord32, COEF_MAX);
130  }
131 }
132 
133 
135 {
136  AC3EncodeContext *s = avctx->priv_data;
137  s->fixed_point = 1;
138  return ff_ac3_encode_init(avctx);
139 }
140 
141 
143  .name = "ac3_fixed",
144  .type = AVMEDIA_TYPE_AUDIO,
145  .id = CODEC_ID_AC3,
146  .priv_data_size = sizeof(AC3EncodeContext),
148  .encode = ff_ac3_fixed_encode_frame,
150  .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
151  .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
152  .priv_class = &ac3enc_class,
153  .channel_layouts = ff_ac3_channel_layouts,
154 };