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• ffmpeg audio decoding providing half the data from original audio in C++

  3 mai 2016, par hockeyislife

  I am trying to write a simple program in C++ that captures audio from a microphone on the computer and encodes it into mp2. Which I was successful in doing, I verified this by saving a mp2 audio file and playing it back in VLC.

  I then decided to see if I could take the encoded audio packets from ffmpeg and convert them back to raw PCM format, and this is where I am having trouble.

  So below is my decoder settings :

  AVCodecID audio_codec_id = AV_CODEC_ID_MP2;
  
  AVCodec * audio_decodec = avcodec_find_decoder(audio_codec_id);
  
  if (!audio_decodec) 
  
  { 
  
      return -1;
  
  }
  
  audio_decodec_ctx = avcodec_alloc_context3(audio_decodec); 
  
  audio_decodec_ctx->bit_rate = 64000;
  
  audio_decodec_ctx->channels = 2;
  
  audio_decodec_ctx->channel_layout = AV_CH_LAYOUT_STEREO;
  
  audio_decodec_ctx->sample_rate = 44100;
  
  audio_decodec_ctx->sample_fmt = AV_SAMPLE_FMT_S16;
  
  
  
  int retval;
  
  if ((retval = avcodec_open2(audio_decodec_ctx, audio_decodec, NULL)) < 0) 
  
  { 
  
      return -1;
  
  }

  Here is my encoder settings, which I made identical :

  AVCodecID audio_codec_id = AV_CODEC_ID_MP2;
  
  AVCodec* audio_codec = avcodec_find_encoder(audio_codec_id);
  
  if (!audio_codec) 
  
  { 
  
      return -1;
  
  }
  
  
  
  // Initialize codec. 
  
  AVCodecContext* audio_codec_ctx = avcodec_alloc_context3(audio_codec);
  
  audio_codec_ctx->bit_rate = 64000;
  
  audio_codec_ctx->channels = 2;
  
  audio_codec_ctx->channel_layout = AV_CH_LAYOUT_STEREO;
  
  audio_codec_ctx->sample_rate = 44100;
  
  audio_codec_ctx->sample_fmt = AV_SAMPLE_FMT_S16;
  
  
  
  int audio_retval;
  
  if ((audio_retval = avcodec_open2(audio_codec_ctx, audio_codec, NULL)) < 0) 
  
  { 
  
      return -1;
  
  }

  As stated previously, the encoding of the audio signal works perfectly, when I try to take the packets that are encoded and attempt to convert them back I am getting only half the data.

  avcodec_encode_audio2(audio_codec_ctx, &audio_pkt, pOutAudioFrame, &got_output);
  
  
  
  if (got_output) 
  
  {
  
      fwrite(audio_pkt.data, 1, audio_pkt.size, f); // MP2 file write which, sounds very nice, which leads me to believe encoding is being done correctly
  
      AVFrame * audio_frame_decode = av_frame_alloc();
  
      avcodec_get_frame_defaults(audio_frame_decode);
  
      int frame_finished = 0;
  
  
  
      avcodec_decode_audio4(audio_decodec_ctx, audio_frame_decode, &frame_finished, &audio_pkt );
  
      if (frame_finished)
  
      {
  
          decoded_size += audio_frame_decode->linesize[0];  // only getting 2304 bytes
  
          av_free_packet(&audio_pkt);
  
      }
  
  }   

  The amount of PCM data being taken is 4608 but after decoding the encoder version I am getting only 2304 bytes. Seems like I have something incorrect but I can’t put my finger on it. Any help would be greatly appreciated.

  Thanks in advance.

• Revision 51875 : Slogan, mise à jour de la description et des auteurs, (google translate ...

  26 septembre 2011, par yffic@… — Log

  Slogan, mise à jour de la description et des auteurs, (google translate pour l’Italien). Kent1, je ne sais pas pour la borne sup si tu as testé sous spip3 ? Moi, pas.

• Revision 1395b56a1d : Add assembly tests for int projections. BUG=https://code.google.com/p/webm/issu

  19 juin 2015, par Frank Galligan

  Changed Paths :
   Modify /test/vp9_avg_test.cc

  
  
  Add assembly tests for int projections.

  BUG=https://code.google.com/p/webm/issues/detail?id=1022

  Change-Id : I5ae4acac39fd75c56d3feff0716cb52133de3b22