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• ClassX installation "codec not found" due to dependencies [migrated]

  25 mars 2014, par khateeb

  ClassX is an interactive lecture streaming system developed in the Electrical Engineering Department at Stanford University.
  Unlike conventional lecture capturing systems, ClassX requires very simple consumer-grade equipment and minimal human operation.

  I faced problems during installing it, I hope you have a solution.

  BTW : I successfully installed it 2 years ago, but now I think the problem as the dependencies and Ubuntu versions are different than the versions we used two years ago.

  Detailed description of the problem :

  • I’m using Ubuntu 12.04
  • I followed the instructions @ ClassX installation guide, and all steps till step 4 are successfully done (the encoder bin file generated).
  • When trying to encode the video using the classX web system, it shows the encoding completed after few seconds.However, there are no tiles generated.

  • I tried to execute the command at CX_log.txt, and the following error appears.

    mahmoud@Mahmoud-HP-Pavilion-dv5-Notebook-PC : $ sudo perl /var/www/ClassXWebSystem/system/publishers/web/actions/encode.pl "/var/www/ClassXWebSystem/content/encoding/FALL_2013_2014/CS106A_FALL_2013_2014/lecSEven" "/var/www/ClassXWebSystem/content/encoding/FALL_2013_2014/CS106A_FALL_2013_2014/.encoding_1372706251" "/var/www/ClassXWebSystem/content/streaming/FALL_2013_2014/CS106A_FALL_2013_2014/lecSEven" "/var/www/ClassXWebSystem/system/publishers/bin" classx y n n
    [sudo] password for mahmoud :
    00068.jpg
    ..
    .
    00068.mp4
    Input #0, mov,mp4,m4a,3gp,3g2,mj2, from ’/var/www/ClassXWebSystem/content/encoding/FALL_2013_2014/CS106A_FALL_2013_2014/.encoding_1372706251/00068.mp4’ :
    Metadata :
    major_brand : isom
    minor_version : 512
    compatible_brands : isomiso2avc1mp41
    encoder : Lavf52.39.0
    Duration : 00:02:30.05, start : 0.000000, bitrate : 8141 kb/s
    Stream #0.0(und) : Video : h264, yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], 8007 kb/s, 29.95 fps, 29.97 tbr, 2997 tbn, 59.94 tbc
    Stream #0.1(und) : Audio : aac, 44100 Hz, stereo, s16, 128 kb/s
    Output #0, mp4, to ’/var/www/ClassXWebSystem/content/encoding/FALL_2013_2014/CS106A_FALL_2013_2014/.encoding_1372706251/stream0.mp4’ :
    Stream #0.0 : Video : [0][0][0][0] / 0x0000, yuv420p, 640x360, q=32-36, 64 kb/s, 90k tbn, 14.99 tbc
    codec not found

• ClassX installation "codec not found" due to dependencies [migrated]

  25 mars 2014, par khateeb

  ClassX is an interactive lecture streaming system developed in the Electrical Engineering Department at Stanford University.
  Unlike conventional lecture capturing systems, ClassX requires very simple consumer-grade equipment and minimal human operation.

  I faced problems during installing it, I hope you have a solution.

  BTW : I successfully installed it 2 years ago, but now I think the problem as the dependencies and Ubuntu versions are different than the versions we used two years ago.

  Detailed description of the problem :

  • I'm using Ubuntu 12.04
  • I followed the instructions @ ClassX installation guide, and all steps till step 4 are successfully done (the encoder bin file generated).
  • When trying to encode the video using the classX web system, it shows the encoding completed after few seconds.However, there are no tiles generated.

  • I tried to execute the command at CX_log.txt, and the following error appears.

    mahmoud@Mahmoud-HP-Pavilion-dv5-Notebook-PC : $ sudo perl /var/www/ClassXWebSystem/system/publishers/web/actions/encode.pl "/var/www/ClassXWebSystem/content/encoding/FALL_2013_2014/CS106A_FALL_2013_2014/lecSEven" "/var/www/ClassXWebSystem/content/encoding/FALL_2013_2014/CS106A_FALL_2013_2014/.encoding_1372706251" "/var/www/ClassXWebSystem/content/streaming/FALL_2013_2014/CS106A_FALL_2013_2014/lecSEven" "/var/www/ClassXWebSystem/system/publishers/bin" classx y n n
    [sudo] password for mahmoud :
    00068.jpg
    ..
    .
    00068.mp4
    Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/var/www/ClassXWebSystem/content/encoding/FALL_2013_2014/CS106A_FALL_2013_2014/.encoding_1372706251/00068.mp4' :
    Metadata :
    major_brand : isom
    minor_version : 512
    compatible_brands : isomiso2avc1mp41
    encoder : Lavf52.39.0
    Duration : 00:02:30.05, start : 0.000000, bitrate : 8141 kb/s
    Stream #0.0(und) : Video : h264, yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], 8007 kb/s, 29.95 fps, 29.97 tbr, 2997 tbn, 59.94 tbc
    Stream #0.1(und) : Audio : aac, 44100 Hz, stereo, s16, 128 kb/s
    Output #0, mp4, to '/var/www/ClassXWebSystem/content/encoding/FALL_2013_2014/CS106A_FALL_2013_2014/.encoding_1372706251/stream0.mp4' :
    Stream #0.0 : Video : [0][0][0][0] / 0x0000, yuv420p, 640x360, q=32-36, 64 kb/s, 90k tbn, 14.99 tbc
    codec not found

• FFmpeg how to apply "aac_adtstoasc" and "h264_mp4toannexb" bitstream filters to transcode to h.264 with AAC

  9 juillet 2015, par larod

  I’ve been struggling with this issue for about a month, I have studied FFmpeg documentation more specifically transcode_aac.c, transcoding.c, decoding_encoding.c and Handbrake’s implementation which is really dense.

  The error that I’m getting is the following : [mp4 @ 0x11102f800] Malformed AAC bitstream detected: use the audio bitstream filter 'aac_adtstoasc' to fix it ('-bsf:a aac_adtstoasc' option with ffmpeg).

  The research I’ve done points to a filter that needs to be implemented.

  FIX:AAC in some container format (FLV, MP4, MKV etc.) need "aac_adtstoasc" bitstream filter (BSF).

  I know I can do the following :

  AVBitStreamFilterContext* aacbsfc =  av_bitstream_filter_init("aac_adtstoasc");

  And then do something like this :

  av_bitstream_filter_filter(aacbsfc, in_stream->codec, NULL, &pkt.data, &pkt.size, pkt.data, pkt.size, 0);

  What eludes me is when to filter the AVPacket, is it before calling av_packet_rescale_ts or inside init_filter. I would greatly appreciate if someone can point me in the right direction. Thanks in advance.

  // Variables
  
  AVFormatContext *_ifmt_ctx, *_ofmt_ctx;
  
  FilteringContext *_filter_ctx;
  
  AVBitStreamFilterContext *_h264bsfc;
  
  AVBitStreamFilterContext *_aacbsfc;
  
  NSURL *_srcURL, *_dstURL;
  
  
  
   - (IBAction)trancode:(id)sender {
  
          NSLog(@"%s %@",__func__, _mediaFile.fsName);
  
          int ret, got_frame;
  
          int (*dec_func)(AVCodecContext *, AVFrame *, int *, const AVPacket *);
  
          unsigned int stream_index, i;
  
          enum AVMediaType type;
  
          AVPacket packet = {.data = NULL, .size = 0};
  
          AVFrame *frame = NULL;
  
          _h264bsfc = av_bitstream_filter_init("h264_mp4toannexb");
  
          _aacbsfc =  av_bitstream_filter_init("aac_adtstoasc");
  
  
  
      _srcURL = [Utility urlFromBookmark:_mediaFile.bookmark];
  
      if ([_srcURL startAccessingSecurityScopedResource]) {
  
          NSString *newFileName = [[_srcURL.lastPathComponent stringByDeletingPathExtension]stringByAppendingPathExtension:@"mp4"];
  
          _dstURL = [NSURL fileURLWithPath:[[_srcURL URLByDeletingLastPathComponent]URLByAppendingPathComponent:newFileName].path isDirectory:NO];
  
  
  
          [AppDelegate ffmpegRegisterAll];
  
  
  
          ret = open_input_file(_srcURL.path.fileSystemRepresentation);
  
          if (ret < 0) {
  
              NSLog(@"Error openning input file.");
  
          }
  
  
  
          ret = open_output_file(_dstURL.path.fileSystemRepresentation);
  
          if (ret < 0) {
  
              NSLog(@"Error openning output file.");
  
          }
  
  
  
          ret = init_filters();
  
          if (ret < 0) {
  
              NSLog(@"Error initializing filters.");
  
          }
  
  
  
          AVBitStreamFilterContext *h264bsfc = av_bitstream_filter_init("h264_mp4toannexb");
  
          AVBitStreamFilterContext* aacbsfc =  av_bitstream_filter_init("aac_adtstoasc");
  
          // Transcode *******************************************************************************
  
          while (1) {
  
              if ((ret = av_read_frame(_ifmt_ctx, &packet)) < 0) {
  
                  break;
  
              }
  
              stream_index = packet.stream_index;
  
              type = _ifmt_ctx->streams[packet.stream_index]->codec->codec_type;
  
              av_log(NULL, AV_LOG_DEBUG, "Demuxer gave frame of stream_index %u\n", stream_index);
  
  
  
  
  
  
  
              if (_filter_ctx[stream_index].filter_graph) {
  
                  av_log(NULL, AV_LOG_DEBUG, "Going to reencode&filter the frame\n");
  
                  frame = av_frame_alloc();
  
                  if (!frame) {
  
                      ret = AVERROR(ENOMEM);
  
                      break;
  
                  }
  
  
  
                  av_packet_rescale_ts(&packet, _ifmt_ctx->streams[stream_index]->time_base, _ifmt_ctx->streams[stream_index]->codec->time_base);
  
                  dec_func = (type == AVMEDIA_TYPE_VIDEO) ? avcodec_decode_video2 : avcodec_decode_audio4;
  
                  ret = dec_func(_ifmt_ctx->streams[stream_index]->codec, frame, &got_frame, &packet);
  
                  if (ret < 0) {
  
                      av_frame_free(&frame);
  
                      av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");
  
                      break;
  
                  }
  
  
  
                  if (got_frame) {
  
                      frame->pts = av_frame_get_best_effort_timestamp(frame);
  
                      ret = filter_encode_write_frame(frame, stream_index);
  
                      av_frame_free(&frame);
  
                      if (ret < 0)
  
                          goto end;
  
                  } else {
  
                      av_frame_free(&frame);
  
                  }
  
              } else {
  
                  /* remux this frame without reencoding */
  
                  av_packet_rescale_ts(&packet,
  
                                       _ifmt_ctx->streams[stream_index]->time_base,
  
                                       _ofmt_ctx->streams[stream_index]->time_base);
  
  
  
                  ret = av_interleaved_write_frame(_ofmt_ctx, &packet);
  
                  if (ret < 0)
  
                      goto end;
  
              }
  
              av_free_packet(&packet);
  
          }
  
          // *****************************************************************************************
  
  
  
          /* flush filters and encoders */
  
          for (i = 0; i < _ifmt_ctx->nb_streams; i++) {
  
              /* flush filter */
  
              if (!_filter_ctx[i].filter_graph)
  
                  continue;
  
              ret = filter_encode_write_frame(NULL, i);
  
              if (ret < 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Flushing filter failed\n");
  
                  goto end;
  
              }
  
  
  
              /* flush encoder */
  
              ret = flush_encoder(i);
  
              if (ret < 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Flushing encoder failed\n");
  
                  goto end;
  
              }
  
          }
  
          av_write_trailer(_ofmt_ctx);
  
          av_bitstream_filter_close(h264bsfc);
  
          av_bitstream_filter_close(aacbsfc);
  
      } else {
  
          NSLog(@"Unable to resolve url for %@",_mediaFile.url.lastPathComponent);
  
      }
  
      [_srcURL stopAccessingSecurityScopedResource];
  
  
  
  end:
  
      av_free_packet(&packet);
  
      av_frame_free(&frame);
  
      for (i = 0; i < _ifmt_ctx->nb_streams; i++) {
  
          avcodec_close(_ifmt_ctx->streams[i]->codec);
  
          if (_ofmt_ctx && _ofmt_ctx->nb_streams > i && _ofmt_ctx->streams[i] && _ofmt_ctx->streams[i]->codec)
  
              avcodec_close(_ofmt_ctx->streams[i]->codec);
  
          if (_filter_ctx && _filter_ctx[i].filter_graph)
  
              avfilter_graph_free(&_filter_ctx[i].filter_graph);
  
      }
  
      av_free(_filter_ctx);
  
      avformat_close_input(&_ifmt_ctx);
  
      if (_ofmt_ctx && !(_ofmt_ctx->oformat->flags & AVFMT_NOFILE))
  
          avio_closep(&_ofmt_ctx->pb);
  
      avformat_free_context(_ofmt_ctx);
  
  }

  The following method is used to open the input file and create the ifmt_ctx.

  int open_input_file(const char *filename) {
  
      int ret;
  
      unsigned int i;
  
  
  
      _ifmt_ctx = NULL;
  
      if ((ret = avformat_open_input(&_ifmt_ctx, filename, NULL, NULL)) < 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
  
          return ret;
  
      }
  
  
  
      if ((ret = avformat_find_stream_info(_ifmt_ctx, NULL)) < 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
  
          return ret;
  
      }
  
  
  
      for (i = 0; i < _ifmt_ctx->nb_streams; i++) {
  
          AVStream *stream;
  
          AVCodecContext *codec_ctx;
  
          stream = _ifmt_ctx->streams[i];
  
          codec_ctx = stream->codec;
  
          /* Reencode video & audio and remux subtitles etc. */
  
          if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO
  
              || codec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
  
              /* Open decoder */
  
              ret = avcodec_open2(codec_ctx,
  
                                  avcodec_find_decoder(codec_ctx->codec_id), NULL);
  
              if (ret < 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Failed to open decoder for stream #%u\n", i);
  
                  return ret;
  
              }
  
          }
  
      }
  
  
  
      // Remove later
  
      av_dump_format(_ifmt_ctx, 0, filename, 0);
  
      return 0;
  
  }

  This method is used to open the output file and create the output format context.

  int open_output_file(const char *filename) {
  
      AVStream *out_stream;
  
      AVStream *in_stream;
  
      AVCodecContext *dec_ctx, *enc_ctx;
  
      AVCodec *encoder;
  
      int ret;
  
      unsigned int i;
  
  
  
      _ofmt_ctx = NULL;
  
      avformat_alloc_output_context2(&_ofmt_ctx, NULL, NULL, filename);
  
      if (!_ofmt_ctx) {
  
          av_log(NULL, AV_LOG_ERROR, "Could not create output context\n");
  
          return AVERROR_UNKNOWN;
  
      }
  
  
  
  
  
      for (i = 0; i < _ifmt_ctx->nb_streams; i++) {
  
          out_stream = avformat_new_stream(_ofmt_ctx, NULL);
  
          if (!out_stream) {
  
              av_log(NULL, AV_LOG_ERROR, "Failed allocating output stream\n");
  
              return AVERROR_UNKNOWN;
  
          }
  
  
  
          in_stream = _ifmt_ctx->streams[i];
  
          dec_ctx = in_stream->codec;
  
          enc_ctx = out_stream->codec;
  
  
  
          if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {
  
              // set video stream
  
              encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
  
              avcodec_get_context_defaults3(enc_ctx, encoder);
  
              av_opt_set(enc_ctx->priv_data, "preset", "slow", 0);
  
              enc_ctx->height = dec_ctx->height;
  
              enc_ctx->width = dec_ctx->width;
  
              enc_ctx->bit_rate = dec_ctx->bit_rate;
  
              enc_ctx->time_base = out_stream->time_base = dec_ctx->time_base;
  
              enc_ctx->pix_fmt = encoder->pix_fmts[0];
  
  
  
              ret = avcodec_open2(enc_ctx, encoder, NULL);
  
              if (ret < 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u\n", i);
  
                  return ret;
  
              }
  
  
  
          } else if (dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
  
              // set audio stream
  
              //encoder = avcodec_find_encoder(AV_CODEC_ID_AAC);
  
              encoder = avcodec_find_encoder_by_name("libfdk_aac");
  
              avcodec_get_context_defaults3(enc_ctx, encoder);
  
              enc_ctx->profile = FF_PROFILE_AAC_HE_V2;
  
              enc_ctx->sample_rate = dec_ctx->sample_rate;
  
              enc_ctx->channel_layout = dec_ctx->channel_layout;
  
              enc_ctx->channels = av_get_channel_layout_nb_channels(enc_ctx->channel_layout);
  
              enc_ctx->sample_fmt = encoder->sample_fmts[0];
  
              enc_ctx->time_base = out_stream->time_base = (AVRational){1, enc_ctx->sample_rate};
  
              enc_ctx->bit_rate = dec_ctx->bit_rate;
  
  
  
              ret = avcodec_open2(enc_ctx, encoder, NULL);
  
              if (ret < 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u\n", i);
  
                  return ret;
  
              }
  
  
  
          } else if (dec_ctx->codec_type == AVMEDIA_TYPE_UNKNOWN) {
  
              // deal with error
  
              av_log(NULL, AV_LOG_FATAL, "Elementary stream #%d is of unknown type, cannot proceed\n", i);
  
              return AVERROR_INVALIDDATA;
  
          } else {
  
              // remux stream
  
              ret = avcodec_copy_context(_ofmt_ctx->streams[i]->codec,
  
                                         _ifmt_ctx->streams[i]->codec);
  
              if (ret < 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Copying stream context failed\n");
  
                  return ret;
  
              }
  
          }
  
  
  
          if (_ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER) {
  
              enc_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
          }
  
      }
  
  
  
      av_dump_format(_ofmt_ctx, 0, filename, 1);
  
  
  
      NSURL *openFileURL = [Utility openPanelAt:[NSURL URLWithString:_dstURL.URLByDeletingLastPathComponent.path]
  
                                      withTitle:@"Transcode File"
  
                                        message:@"Please allow Maví to create the new file."
  
                                      andPrompt:@"Grant Access"];
  
  
  
      openFileURL = [openFileURL URLByAppendingPathComponent:_dstURL.lastPathComponent isDirectory:NO];
  
      if (!(_ofmt_ctx->oformat->flags & AVFMT_NOFILE)) {
  
          ret = avio_open(&_ofmt_ctx->pb, openFileURL.fileSystemRepresentation, AVIO_FLAG_WRITE);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Could not open output file '%s'", filename);
  
              return ret;
  
          }
  
      }
  
  
  
      /* init muxer, write output file header */
  
      ret = avformat_write_header(_ofmt_ctx, NULL);
  
      if (ret < 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Error occurred when opening output file\n");
  
          return ret;
  
      }
  
  
  
      return 0;
  
  }

  These two methods deal with initialising the filters and filtering.

  int init_filters(void) {
  
      const char *filter_spec;
  
      unsigned int i;
  
      int ret;
  
      _filter_ctx = av_malloc_array(_ifmt_ctx->nb_streams, sizeof(*_filter_ctx));
  
      if (!_filter_ctx)
  
          return AVERROR(ENOMEM);
  
  
  
      for (i = 0; i < _ifmt_ctx->nb_streams; i++) {
  
          _filter_ctx[i].buffersrc_ctx  = NULL;
  
          _filter_ctx[i].buffersink_ctx = NULL;
  
          _filter_ctx[i].filter_graph   = NULL;
  
          if (!(_ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
  
                || _ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO))
  
              continue;
  
  
  
  
  
          if (_ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
  
              filter_spec = "null"; /* passthrough (dummy) filter for video */
  
          else
  
              filter_spec = "anull"; /* passthrough (dummy) filter for audio */
  
          ret = init_filter(&_filter_ctx[i], _ifmt_ctx->streams[i]->codec,
  
                            _ofmt_ctx->streams[i]->codec, filter_spec);
  
          if (ret)
  
              return ret;
  
      }
  
      return 0;
  
  }
  
  int init_filter(FilteringContext* fctx, AVCodecContext *dec_ctx, AVCodecContext *enc_ctx, const char *filter_spec) {
  
      char args[512];
  
      int ret = 0;
  
      AVFilter *buffersrc = NULL;
  
      AVFilter *buffersink = NULL;
  
      AVFilterContext *buffersrc_ctx = NULL;
  
      AVFilterContext *buffersink_ctx = NULL;
  
      AVFilterInOut *outputs = avfilter_inout_alloc();
  
      AVFilterInOut *inputs  = avfilter_inout_alloc();
  
      AVFilterGraph *filter_graph = avfilter_graph_alloc();
  
  
  
      if (!outputs || !inputs || !filter_graph) {
  
          ret = AVERROR(ENOMEM);
  
          goto end;
  
      }
  
  
  
      if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {
  
          buffersrc = avfilter_get_by_name("buffer");
  
          buffersink = avfilter_get_by_name("buffersink");
  
          if (!buffersrc || !buffersink) {
  
              av_log(NULL, AV_LOG_ERROR, "filtering source or sink element not found\n");
  
              ret = AVERROR_UNKNOWN;
  
              goto end;
  
          }
  
  
  
          snprintf(args, sizeof(args),
  
                   "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
  
                   dec_ctx->width, dec_ctx->height, dec_ctx->pix_fmt,
  
                   dec_ctx->time_base.num, dec_ctx->time_base.den,
  
                   dec_ctx->sample_aspect_ratio.num,
  
                   dec_ctx->sample_aspect_ratio.den);
  
  
  
          ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
  
                                             args, NULL, filter_graph);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Cannot create buffer source\n");
  
              goto end;
  
          }
  
  
  
          ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
  
                                             NULL, NULL, filter_graph);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Cannot create buffer sink\n");
  
              goto end;
  
          }
  
  
  
          ret = av_opt_set_bin(buffersink_ctx, "pix_fmts",
  
                               (uint8_t*)&enc_ctx->pix_fmt, sizeof(enc_ctx->pix_fmt),
  
                               AV_OPT_SEARCH_CHILDREN);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Cannot set output pixel format\n");
  
              goto end;
  
          }
  
      } else if (dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
  
          buffersrc = avfilter_get_by_name("abuffer");
  
          buffersink = avfilter_get_by_name("abuffersink");
  
          if (!buffersrc || !buffersink) {
  
              av_log(NULL, AV_LOG_ERROR, "filtering source or sink element not found\n");
  
              ret = AVERROR_UNKNOWN;
  
              goto end;
  
          }
  
  
  
          if (!dec_ctx->channel_layout)
  
              dec_ctx->channel_layout =
  
              av_get_default_channel_layout(dec_ctx->channels);
  
          snprintf(args, sizeof(args),
  
                   "time_base=%d/%d:sample_rate=%d:sample_fmt=%s:channel_layout=0x%"PRIx64,
  
                   dec_ctx->time_base.num, dec_ctx->time_base.den, dec_ctx->sample_rate,
  
                   av_get_sample_fmt_name(dec_ctx->sample_fmt),
  
                   dec_ctx->channel_layout);
  
          ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
  
                                             args, NULL, filter_graph);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer source\n");
  
              goto end;
  
          }
  
  
  
          ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
  
                                             NULL, NULL, filter_graph);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer sink\n");
  
              goto end;
  
          }
  
  
  
          ret = av_opt_set_bin(buffersink_ctx, "sample_fmts",
  
                               (uint8_t*)&enc_ctx->sample_fmt, sizeof(enc_ctx->sample_fmt),
  
                               AV_OPT_SEARCH_CHILDREN);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Cannot set output sample format\n");
  
              goto end;
  
          }
  
  
  
          ret = av_opt_set_bin(buffersink_ctx, "channel_layouts",
  
                               (uint8_t*)&enc_ctx->channel_layout,
  
                               sizeof(enc_ctx->channel_layout), AV_OPT_SEARCH_CHILDREN);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Cannot set output channel layout\n");
  
              goto end;
  
          }
  
  
  
          ret = av_opt_set_bin(buffersink_ctx, "sample_rates",
  
                               (uint8_t*)&enc_ctx->sample_rate, sizeof(enc_ctx->sample_rate),
  
                               AV_OPT_SEARCH_CHILDREN);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Cannot set output sample rate\n");
  
              goto end;
  
          }
  
      } else {
  
          ret = AVERROR_UNKNOWN;
  
          goto end;
  
      }
  
  
  
      /* Endpoints for the filter graph. */
  
      outputs->name       = av_strdup("in");
  
      outputs->filter_ctx = buffersrc_ctx;
  
      outputs->pad_idx    = 0;
  
      outputs->next       = NULL;
  
  
  
      inputs->name       = av_strdup("out");
  
      inputs->filter_ctx = buffersink_ctx;
  
      inputs->pad_idx    = 0;
  
      inputs->next       = NULL;
  
  
  
      if (!outputs->name || !inputs->name) {
  
          ret = AVERROR(ENOMEM);
  
          goto end;
  
      }
  
  
  
      if ((ret = avfilter_graph_parse_ptr(filter_graph, filter_spec,
  
                                          &inputs, &outputs, NULL)) < 0)
  
          goto end;
  
  
  
      if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)
  
          goto end;
  
  
  
      /* Fill FilteringContext */
  
      fctx->buffersrc_ctx = buffersrc_ctx;
  
      fctx->buffersink_ctx = buffersink_ctx;
  
      fctx->filter_graph = filter_graph;
  
  
  
  end:
  
      avfilter_inout_free(&inputs);
  
      avfilter_inout_free(&outputs);
  
  
  
      return ret;
  
  }

  Finally these two methods take care of writing the frames.

  int encode_write_frame(AVFrame *filt_frame, unsigned int stream_index, int *got_frame) {
  
      int ret;
  
      int got_frame_local;
  
      AVPacket enc_pkt;
  
      int (*enc_func)(AVCodecContext *, AVPacket *, const AVFrame *, int *) =
  
      (_ifmt_ctx->streams[stream_index]->codec->codec_type ==
  
       AVMEDIA_TYPE_VIDEO) ? avcodec_encode_video2 : avcodec_encode_audio2;
  
  
  
      if (!got_frame)
  
          got_frame = &got_frame_local;
  
  
  
      av_log(NULL, AV_LOG_INFO, "Encoding frame\n");
  
      /* encode filtered frame */
  
      enc_pkt.data = NULL;
  
      enc_pkt.size = 0;
  
      av_init_packet(&enc_pkt);
  
      ret = enc_func(_ofmt_ctx->streams[stream_index]->codec, &enc_pkt,
  
                     filt_frame, got_frame);
  
      av_frame_free(&filt_frame);
  
      if (ret < 0)
  
          return ret;
  
      if (!(*got_frame))
  
          return 0;
  
  
  
      /* prepare packet for muxing */
  
      enc_pkt.stream_index = stream_index;
  
      av_packet_rescale_ts(&enc_pkt,
  
                           _ofmt_ctx->streams[stream_index]->codec->time_base,
  
                           _ofmt_ctx->streams[stream_index]->time_base);
  
  
  
      av_log(NULL, AV_LOG_DEBUG, "Muxing frame\n");
  
      /* mux encoded frame */
  
      ret = av_interleaved_write_frame(_ofmt_ctx, &enc_pkt);
  
      return ret;
  
  }
  
  int filter_encode_write_frame(AVFrame *frame, unsigned int stream_index)
  
  {
  
      int ret;
  
      AVFrame *filt_frame;
  
  
  
      av_log(NULL, AV_LOG_INFO, "Pushing decoded frame to filters\n");
  
      /* push the decoded frame into the filtergraph */
  
      ret = av_buffersrc_add_frame_flags(_filter_ctx[stream_index].buffersrc_ctx,
  
                                         frame, 0);
  
      if (ret < 0) {
  
          av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");
  
          return ret;
  
      }
  
  
  
      /* pull filtered frames from the filtergraph */
  
      while (1) {
  
          filt_frame = av_frame_alloc();
  
          if (!filt_frame) {
  
              ret = AVERROR(ENOMEM);
  
              break;
  
          }
  
          av_log(NULL, AV_LOG_INFO, "Pulling filtered frame from filters\n");
  
          ret = av_buffersink_get_frame(_filter_ctx[stream_index].buffersink_ctx,
  
                                        filt_frame);
  
          if (ret < 0) {
  
              /* if no more frames for output - returns AVERROR(EAGAIN)
  
               * if flushed and no more frames for output - returns AVERROR_EOF
  
               * rewrite retcode to 0 to show it as normal procedure completion
  
               */
  
              if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
  
                  ret = 0;
  
              av_frame_free(&filt_frame);
  
              break;
  
          }
  
  
  
          filt_frame->pict_type = AV_PICTURE_TYPE_NONE;
  
          ret = encode_write_frame(filt_frame, stream_index, NULL);
  
          if (ret < 0)
  
              break;
  
      }
  
  
  
      return ret;
  
  }