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ffmpeg / libavcodec / ac3enc_fixed.c @ 6ad2bafc

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/*
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 * The simplest AC-3 encoder
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 * Copyright (c) 2000 Fabrice Bellard
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 * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
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 * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
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 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * Libav is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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/**
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 * @file
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 * fixed-point AC-3 encoder.
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 */
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#define CONFIG_FFT_FLOAT 0
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#undef CONFIG_AC3ENC_FLOAT
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#include "ac3enc.c"
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/**
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 * Finalize MDCT and free allocated memory.
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 */
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static av_cold void mdct_end(AC3MDCTContext *mdct)
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{
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    ff_mdct_end(&mdct->fft);
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}
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/**
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 * Initialize MDCT tables.
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 * @param nbits log2(MDCT size)
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 */
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static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct,
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                             int nbits)
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{
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    int ret = ff_mdct_init(&mdct->fft, nbits, 0, 1.0);
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    mdct->window = ff_ac3_window;
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    return ret;
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}
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/**
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 * Apply KBD window to input samples prior to MDCT.
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 */
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static void apply_window(DSPContext *dsp, int16_t *output, const int16_t *input,
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                         const int16_t *window, unsigned int len)
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{
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    dsp->apply_window_int16(output, input, window, len);
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}
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/**
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 * Calculate the log2() of the maximum absolute value in an array.
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 * @param tab input array
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 * @param n   number of values in the array
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 * @return    log2(max(abs(tab[])))
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 */
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static int log2_tab(AC3EncodeContext *s, int16_t *src, int len)
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{
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    int v = s->ac3dsp.ac3_max_msb_abs_int16(src, len);
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    return av_log2(v);
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}
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/**
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 * Normalize the input samples to use the maximum available precision.
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 * This assumes signed 16-bit input samples.
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 *
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 * @return exponent shift
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 */
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static int normalize_samples(AC3EncodeContext *s)
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{
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    int v = 14 - log2_tab(s, s->windowed_samples, AC3_WINDOW_SIZE);
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    if (v > 0)
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        s->ac3dsp.ac3_lshift_int16(s->windowed_samples, AC3_WINDOW_SIZE, v);
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    /* +6 to right-shift from 31-bit to 25-bit */
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    return v + 6;
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}
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/**
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 * Scale MDCT coefficients to 25-bit signed fixed-point.
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 */
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static void scale_coefficients(AC3EncodeContext *s)
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{
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    int blk, ch;
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    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
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        AC3Block *block = &s->blocks[blk];
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        for (ch = 0; ch < s->channels; ch++) {
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            s->ac3dsp.ac3_rshift_int32(block->mdct_coef[ch], AC3_MAX_COEFS,
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                                       block->coeff_shift[ch]);
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        }
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    }
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}
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AVCodec ff_ac3_fixed_encoder = {
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    "ac3_fixed",
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    AVMEDIA_TYPE_AUDIO,
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    CODEC_ID_AC3,
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    sizeof(AC3EncodeContext),
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    ac3_encode_init,
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    ac3_encode_frame,
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    ac3_encode_close,
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    NULL,
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    .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
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    .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
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    .priv_class = &ac3enc_class,
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    .channel_layouts = ac3_channel_layouts,
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};