FFmpeg/libavcodec/ac3enc_float.c

/*
 * The simplest AC-3 encoder
 * Copyright (c) 2000 Fabrice Bellard
 * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
 * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * floating-point AC-3 encoder.
 */

#define CONFIG_AC3ENC_FLOAT 1
#include "ac3enc.c"


/**
 * Finalize MDCT and free allocated memory.
 */
static av_cold void mdct_end(AC3MDCTContext *mdct)
{
    ff_mdct_end(&mdct->fft);
    av_freep(&mdct->window);
}


/**
 * Initialize MDCT tables.
 * @param nbits log2(MDCT size)
 */
static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct,
                             int nbits)
{
    float *window;
    int n, n2;

    n  = 1 << nbits;
    n2 = n >> 1;

    window = av_malloc(n2 * sizeof(*window));
    if (!window) {
        av_log(avctx, AV_LOG_ERROR, "Cannot allocate memory.\n");
        return AVERROR(ENOMEM);
    }
    ff_kbd_window_init(window, 5.0, n2);
    mdct->window = window;

    return ff_mdct_init(&mdct->fft, nbits, 0, -2.0 / n);
}


/**
 * Calculate a 512-point MDCT
 * @param out 256 output frequency coefficients
 * @param in  512 windowed input audio samples
 */
static void mdct512(AC3MDCTContext *mdct, float *out, float *in)
{
    ff_mdct_calc(&mdct->fft, out, in);
}


/**
 * Apply KBD window to input samples prior to MDCT.
 */
static void apply_window(float *output, const float *input,
                         const float *window, int n)
{
    int i;
    int n2 = n >> 1;

    for (i = 0; i < n2; i++) {
        output[i]     = input[i]     * window[i];
        output[n-i-1] = input[n-i-1] * window[i];
    }
}


/**
 * Normalize the input samples to use the maximum available precision.
 */
static int normalize_samples(AC3EncodeContext *s)
{
    /* Normalization is not needed for floating-point samples, so just return 0 */
    return 0;
}


/**
 * Scale MDCT coefficients from float to 24-bit fixed-point.
 */
static void scale_coefficients(AC3EncodeContext *s)
{
    int i;
    for (i = 0; i < AC3_MAX_COEFS * AC3_MAX_BLOCKS * s->channels; i++)
        s->fixed_coef_buffer[i] = SCALE_FLOAT(s->mdct_coef_buffer[i], 24);
}


AVCodec ac3_encoder = {
    "ac3",
    AVMEDIA_TYPE_AUDIO,
    CODEC_ID_AC3,
    sizeof(AC3EncodeContext),
    ac3_encode_init,
    ac3_encode_frame,
    ac3_encode_close,
    NULL,
    .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_FLT,AV_SAMPLE_FMT_NONE},
    .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
    .channel_layouts = ac3_channel_layouts,
};