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  1. /*
  2.  * RFC 3389 comfort noise generator
  3.  * Copyright (c) 2012 Martin Storsjo
  4.  *
  5.  * This file is part of FFmpeg.
  6.  *
  7.  * FFmpeg is free software; you can redistribute it and/or
  8.  * modify it under the terms of the GNU Lesser General Public
  9.  * License as published by the Free Software Foundation; either
  10.  * version 2.1 of the License, or (at your option) any later version.
  11.  *
  12.  * FFmpeg is distributed in the hope that it will be useful,
  13.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15.  * Lesser General Public License for more details.
  16.  *
  17.  * You should have received a copy of the GNU Lesser General Public
  18.  * License along with FFmpeg; if not, write to the Free Software
  19.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20.  */
  21.  
  22. #include <math.h>
  23.  
  24. #include "libavutil/common.h"
  25. #include "avcodec.h"
  26. #include "internal.h"
  27. #include "lpc.h"
  28.  
  29. typedef struct CNGContext {
  30.     LPCContext lpc;
  31.     int order;
  32.     int32_t *samples32;
  33.     double *ref_coef;
  34. } CNGContext;
  35.  
  36. static av_cold int cng_encode_close(AVCodecContext *avctx)
  37. {
  38.     CNGContext *p = avctx->priv_data;
  39.     ff_lpc_end(&p->lpc);
  40.     av_free(p->samples32);
  41.     av_free(p->ref_coef);
  42.     return 0;
  43. }
  44.  
  45. static av_cold int cng_encode_init(AVCodecContext *avctx)
  46. {
  47.     CNGContext *p = avctx->priv_data;
  48.     int ret;
  49.  
  50.     if (avctx->channels != 1) {
  51.         av_log(avctx, AV_LOG_ERROR, "Only mono supported\n");
  52.         return AVERROR(EINVAL);
  53.     }
  54.  
  55.     avctx->frame_size = 640;
  56.     p->order = 10;
  57.     if ((ret = ff_lpc_init(&p->lpc, avctx->frame_size, p->order, FF_LPC_TYPE_LEVINSON)) < 0)
  58.         return ret;
  59.     p->samples32 = av_malloc(avctx->frame_size * sizeof(*p->samples32));
  60.     p->ref_coef = av_malloc(p->order * sizeof(*p->ref_coef));
  61.     if (!p->samples32 || !p->ref_coef) {
  62.         cng_encode_close(avctx);
  63.         return AVERROR(ENOMEM);
  64.     }
  65.  
  66.     return 0;
  67. }
  68.  
  69. static int cng_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
  70.                             const AVFrame *frame, int *got_packet_ptr)
  71. {
  72.     CNGContext *p = avctx->priv_data;
  73.     int ret, i;
  74.     double energy = 0;
  75.     int qdbov;
  76.     int16_t *samples = (int16_t*) frame->data[0];
  77.  
  78.     if ((ret = ff_alloc_packet(avpkt, 1 + p->order))) {
  79.         av_log(avctx, AV_LOG_ERROR, "Error getting output packet\n");
  80.         return ret;
  81.     }
  82.  
  83.     for (i = 0; i < frame->nb_samples; i++) {
  84.         p->samples32[i] = samples[i];
  85.         energy += samples[i] * samples[i];
  86.     }
  87.     energy /= frame->nb_samples;
  88.     if (energy > 0) {
  89.         double dbov = 10 * log10(energy / 1081109975);
  90.         qdbov = av_clip(-floor(dbov), 0, 127);
  91.     } else {
  92.         qdbov = 127;
  93.     }
  94.     ret = ff_lpc_calc_ref_coefs(&p->lpc, p->samples32, p->order, p->ref_coef);
  95.     avpkt->data[0] = qdbov;
  96.     for (i = 0; i < p->order; i++)
  97.         avpkt->data[1 + i] = p->ref_coef[i] * 127 + 127;
  98.  
  99.     *got_packet_ptr = 1;
  100.     avpkt->size = 1 + p->order;
  101.  
  102.     return 0;
  103. }
  104.  
  105. AVCodec ff_comfortnoise_encoder = {
  106.     .name           = "comfortnoise",
  107.     .long_name      = NULL_IF_CONFIG_SMALL("RFC 3389 comfort noise generator"),
  108.     .type           = AVMEDIA_TYPE_AUDIO,
  109.     .id             = AV_CODEC_ID_COMFORT_NOISE,
  110.     .priv_data_size = sizeof(CNGContext),
  111.     .init           = cng_encode_init,
  112.     .encode2        = cng_encode_frame,
  113.     .close          = cng_encode_close,
  114.     .sample_fmts    = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_S16,
  115.                                                      AV_SAMPLE_FMT_NONE },
  116. };
  117.