text: /*
   * RFC 3389 comfort noise generator
   * Copyright (c) 2012 Martin Storsjo
   *
   * 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
   */
  
  #include <math.h>
  
  #include "libavutil/common.h"
  #include "avcodec.h"
  #include "internal.h"
  #include "lpc.h"
  
  typedef struct CNGContext {
      LPCContext lpc;
      int order;
      int32_t *samples32;
      double *ref_coef;
  } CNGContext;
  
  static av_cold int cng_encode_close(AVCodecContext *avctx)
  {
      CNGContext *p = avctx->priv_data;
      ff_lpc_end(&p->lpc);
      av_free(p->samples32);
      av_free(p->ref_coef);
      return 0;
  }
  
  static av_cold int cng_encode_init(AVCodecContext *avctx)
  {
      CNGContext *p = avctx->priv_data;
      int ret;
  
      if (avctx->channels != 1) {
          av_log(avctx, AV_LOG_ERROR, "Only mono supported\n");
          return AVERROR(EINVAL);
      }
  
      avctx->frame_size = 640;
      p->order = 10;
      if ((ret = ff_lpc_init(&p->lpc, avctx->frame_size, p->order, FF_LPC_TYPE_LEVINSON)) < 0)
          return ret;
      p->samples32 = av_malloc_array(avctx->frame_size, sizeof(*p->samples32));
      p->ref_coef = av_malloc_array(p->order, sizeof(*p->ref_coef));
      if (!p->samples32 || !p->ref_coef) {
          cng_encode_close(avctx);
          return AVERROR(ENOMEM);
      }
  
      return 0;
  }
  
  static int cng_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
                              const AVFrame *frame, int *got_packet_ptr)
  {
      CNGContext *p = avctx->priv_data;
      int ret, i;
      double energy = 0;
      int qdbov;
      int16_t *samples = (int16_t*) frame->data[0];
  
      if ((ret = ff_alloc_packet(avpkt, 1 + p->order))) {
          av_log(avctx, AV_LOG_ERROR, "Error getting output packet\n");
          return ret;
      }
  
      for (i = 0; i < frame->nb_samples; i++) {
          p->samples32[i] = samples[i];
          energy += samples[i] * samples[i];
      }
      energy /= frame->nb_samples;
      if (energy > 0) {
          double dbov = 10 * log10(energy / 1081109975);
          qdbov = av_clip(-floor(dbov), 0, 127);
      } else {
          qdbov = 127;
      }
      ret = ff_lpc_calc_ref_coefs(&p->lpc, p->samples32, p->order, p->ref_coef);
      avpkt->data[0] = qdbov;
      for (i = 0; i < p->order; i++)
          avpkt->data[1 + i] = p->ref_coef[i] * 127 + 127;
  
      *got_packet_ptr = 1;
      avpkt->size = 1 + p->order;
  
      return 0;
  }
  
  AVCodec ff_comfortnoise_encoder = {
  	.name           = "comfortnoise",
      .long_name      = NULL_IF_CONFIG_SMALL("RFC 3389 comfort noise generator"),
      .type           = AVMEDIA_TYPE_AUDIO,
      .id             = AV_CODEC_ID_COMFORT_NOISE,
      .priv_data_size = sizeof(CNGContext),
      .init           = cng_encode_init,
      .encode2        = cng_encode_frame,
      .close          = cng_encode_close,
      .sample_fmts    = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_S16,
                                                       AV_SAMPLE_FMT_NONE },
  };
  