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ffmpeg / libavcodec / ac3enc_float.c @ 26f548bb

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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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 * floating-point AC-3 encoder.
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 */
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#define CONFIG_AC3ENC_FLOAT 1
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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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    av_freep(&mdct->window);
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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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    float *window;
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    int i, n, n2;
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    n  = 1 << nbits;
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    n2 = n >> 1;
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    window = av_malloc(n * sizeof(*window));
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    if (!window) {
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        av_log(avctx, AV_LOG_ERROR, "Cannot allocate memory.\n");
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        return AVERROR(ENOMEM);
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    }
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    ff_kbd_window_init(window, 5.0, n2);
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    for (i = 0; i < n2; i++)
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        window[n-1-i] = window[i];
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    mdct->window = window;
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    return ff_mdct_init(&mdct->fft, nbits, 0, -2.0 / n);
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}
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/**
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 * Calculate a 512-point MDCT
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 * @param out 256 output frequency coefficients
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 * @param in  512 windowed input audio samples
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 */
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static void mdct512(AC3MDCTContext *mdct, float *out, float *in)
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{
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    mdct->fft.mdct_calc(&mdct->fft, out, in);
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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, float *output, const float *input,
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                         const float *window, int n)
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{
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    dsp->vector_fmul(output, input, window, n);
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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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 */
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static int normalize_samples(AC3EncodeContext *s)
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{
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    /* Normalization is not needed for floating-point samples, so just return 0 */
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    return 0;
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}
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/**
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 * Scale MDCT coefficients from float to 24-bit fixed-point.
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 */
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static void scale_coefficients(AC3EncodeContext *s)
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{
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    s->ac3dsp.float_to_fixed24(s->fixed_coef_buffer, s->mdct_coef_buffer,
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                               AC3_MAX_COEFS * AC3_MAX_BLOCKS * s->channels);
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}
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AVCodec ff_ac3_encoder = {
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    "ac3",
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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_FLT,AV_SAMPLE_FMT_NONE},
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    .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
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    .channel_layouts = ac3_channel_layouts,
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};