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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 FFmpeg.
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+ *
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+ * FFmpeg 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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+ * FFmpeg 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 FFmpeg; 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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+/**
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+ * @file
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+ * floating-point AC-3 encoder.
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+ */
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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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+
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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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+
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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 n, n2;
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+
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+ n = 1 << nbits;
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+ n2 = n >> 1;
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+
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+ window = av_malloc(n2 * 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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+ mdct->window = window;
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+
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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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+
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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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+ ff_mdct_calc(&mdct->fft, out, in);
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+}
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+
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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(float *output, const float *input,
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+ const float *window, int n)
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+{
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+ int i;
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+ int n2 = n >> 1;
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+
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+ for (i = 0; i < n2; i++) {
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+ output[i] = input[i] * window[i];
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+ output[n-i-1] = input[n-i-1] * window[i];
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+ }
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+}
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+
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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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+
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+AVCodec 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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+};
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Justin Ruggles