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>
7 * This file is part of Libav.
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.
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.
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
26 * fixed-point AC-3 encoder.
29 #define CONFIG_FFT_FLOAT 0
30 #undef CONFIG_AC3ENC_FLOAT
33 #define AC3ENC_TYPE AC3ENC_TYPE_AC3_FIXED
34 #include "ac3enc_opts_template.c"
35 static AVClass ac3enc_class = { "Fixed-Point AC-3 Encoder", av_default_item_name,
36 ac3fixed_options, LIBAVUTIL_VERSION_INT };
38 #include "ac3enc_template.c"
42 * Finalize MDCT and free allocated memory.
44 av_cold void AC3_NAME(mdct_end)(AC3EncodeContext *s)
46 ff_mdct_end(&s->mdct);
51 * Initialize MDCT tables.
52 * @param nbits log2(MDCT size)
54 av_cold int AC3_NAME(mdct_init)(AC3EncodeContext *s)
56 int ret = ff_mdct_init(&s->mdct, 9, 0, -1.0);
57 s->mdct_window = ff_ac3_window;
63 * Apply KBD window to input samples prior to MDCT.
65 static void apply_window(DSPContext *dsp, int16_t *output, const int16_t *input,
66 const int16_t *window, unsigned int len)
68 dsp->apply_window_int16(output, input, window, len);
73 * Normalize the input samples to use the maximum available precision.
74 * This assumes signed 16-bit input samples.
76 * @return exponent shift
78 static int normalize_samples(AC3EncodeContext *s)
80 int v = s->ac3dsp.ac3_max_msb_abs_int16(s->windowed_samples, AC3_WINDOW_SIZE);
83 s->ac3dsp.ac3_lshift_int16(s->windowed_samples, AC3_WINDOW_SIZE, v);
84 /* +6 to right-shift from 31-bit to 25-bit */
90 * Scale MDCT coefficients to 25-bit signed fixed-point.
92 static void scale_coefficients(AC3EncodeContext *s)
96 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
97 AC3Block *block = &s->blocks[blk];
98 for (ch = 1; ch <= s->channels; ch++) {
99 s->ac3dsp.ac3_rshift_int32(block->mdct_coef[ch], AC3_MAX_COEFS,
100 block->coeff_shift[ch]);
107 * Clip MDCT coefficients to allowable range.
109 static void clip_coefficients(DSPContext *dsp, int32_t *coef, unsigned int len)
111 dsp->vector_clip_int32(coef, coef, COEF_MIN, COEF_MAX, len);
115 static av_cold int ac3_fixed_encode_init(AVCodecContext *avctx)
117 AC3EncodeContext *s = avctx->priv_data;
119 return ff_ac3_encode_init(avctx);
123 AVCodec ff_ac3_fixed_encoder = {
127 sizeof(AC3EncodeContext),
128 ac3_fixed_encode_init,
129 ff_ac3_fixed_encode_frame,
132 .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
133 .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
134 .priv_class = &ac3enc_class,
135 .channel_layouts = ff_ac3_channel_layouts,