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
35 * Finalize MDCT and free allocated memory.
37 static av_cold void mdct_end(AC3MDCTContext *mdct)
39 ff_fft_end(&mdct->fft);
44 * Initialize MDCT tables.
45 * @param nbits log2(MDCT size)
47 static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct,
50 int ret = ff_mdct_init(&mdct->fft, nbits, 0, 1.0);
51 mdct->window = ff_ac3_window;
57 * Apply KBD window to input samples prior to MDCT.
59 static void apply_window(DSPContext *dsp, int16_t *output, const int16_t *input,
60 const int16_t *window, unsigned int len)
62 dsp->apply_window_int16(output, input, window, len);
67 * Calculate the log2() of the maximum absolute value in an array.
68 * @param tab input array
69 * @param n number of values in the array
70 * @return log2(max(abs(tab[])))
72 static int log2_tab(AC3EncodeContext *s, int16_t *src, int len)
74 int v = s->ac3dsp.ac3_max_msb_abs_int16(src, len);
80 * Normalize the input samples to use the maximum available precision.
81 * This assumes signed 16-bit input samples.
83 * @return exponent shift
85 static int normalize_samples(AC3EncodeContext *s)
87 int v = 14 - log2_tab(s, s->windowed_samples, AC3_WINDOW_SIZE);
89 s->ac3dsp.ac3_lshift_int16(s->windowed_samples, AC3_WINDOW_SIZE, v);
90 /* +6 to right-shift from 31-bit to 25-bit */
96 * Scale MDCT coefficients to 25-bit signed fixed-point.
98 static void scale_coefficients(AC3EncodeContext *s)
102 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
103 AC3Block *block = &s->blocks[blk];
104 for (ch = 0; ch < s->channels; ch++) {
105 s->ac3dsp.ac3_rshift_int32(block->mdct_coef[ch], AC3_MAX_COEFS,
106 block->coeff_shift[ch]);
112 AVCodec ff_ac3_fixed_encoder = {
116 sizeof(AC3EncodeContext),
121 .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
122 .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
123 .priv_class = &ac3enc_class,
124 .channel_layouts = ac3_channel_layouts,