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• Capture desktop screens including audio with ffmpeg

  9 mars 2019, par klaus

  After referring to the official documentation and one other blog post, I now have following script :

  A="$(pacmd list-sources | grep -PB 1 "analog.*monitor>" | head -n 1 | perl -pe 's/.* //g')"
  
  F="/home/enan/Videos/$(date --iso-8601=minutes | perl -pe 's/[^0-9]+//g').mkv"
  
  V="$(xdpyinfo | grep dimensions | perl -pe 's/.* ([0-9]+x[0-9]+) .*/$1/g')"
  
  ffmpeg -video_size "$V" -framerate 25 -f x11grab -i :0.0 -f pulse -i "$A" -f pulse -i default \
  
      -filter_complex amerge -ac 1 -preset veryfast "$F"

  Basically that script results into the following command :

  ffmpeg -video_size 1366x768 -framerate 25 -f x11grab -i :0.0 -f pulse -ac 2 -i default output.mkv

  In this case, with -ac 2, the audio that gets added with the captured video is of some mic. I’m using a laptop and don’t have a mic, so I don’t exactly know which device the outside sounds get added from but it does. But no audio from the main audio that I can hear through the headphone jack doesn’t get added to the video.

  If I use -ac 1 instead, the video now gets the outside audio as well as the internal audio. That’s good. But how do I restrict the video to only add internal audio, not add audio gotten from mic or something similar.

  I don’t know if it’ll help, but adding it anyway. From man mpv :

         -ac[:stream_specifier] channels (input/output,per-stream)
  
             Set the number of audio channels. For output streams it is set by
  
             default to the number of input audio channels. For input streams this
  
             option only makes sense for audio grabbing devices and raw demuxers and
  
             is mapped to the corresponding demuxer options.

• FFMPEG memory leak on FLV video frame decoding

  10 août 2014, par Michael IV

  I am decoding FLV video on Windows using FFMPEG latest dev version(20140810) .Monitoring memory consumption of my program process I found the memory footprint constantly increasing.I do packet deallocation and also tried to delete and then reallocate the AVFrame anew on each decode.But it doesn’t help.I read on some threads people pointing out there is an internal memory leak in H264 decoder but I have seen no official confirmation of it nor any solution.
  Here is how I decode a frame :

  AVPacket packet;
  
  av_read_frame(_ifmt_ctx, &packet);
  
  
  
  if (packet.stream_index == _in_video_stream->index) 
  
  {
  
      int isGotVideoFrame = 0;
  
  
  
      // Decode video frame
  
      ret = avcodec_decode_video2(_dec_in_video_ctx, _src_video_frame,
  
                     &isGotVideoFrame, &packet);
  
  
  
      if (1 == isGotVideoFrame) 
  
      {
  
          sws_scale(_sws_ctx, (const uint8_t * const*) _src_video_frame->data,
  
                    _src_video_frame->linesize, 0,_inVideoHeight, 
  
                    _dst_video_frame->data, _dst_video_frame->linesize);
  
  
  
          uint8_t* dest = new uint8_t[_numBytes];
  
          memcpy(dest, _dst_video_frame->data[0], _numBytes);
  
  
  
          av_free_packet(&packet);
  
          _frames_cache.push_back(dest);
  
      }
  
  
  
      av_frame_unref(_src_video_frame);
  
      av_frame_free(&_src_video_frame);
  
      _src_video_frame = av_frame_alloc();
  
  }

  Then in another place on each frame I delete ’dest’ from the vector :

      uint8_t * fr = _frames_cache.front();
  
      _frames_cache.erase(_frames_cache.begin());
  
      delete [] fr ;

• c++ ffmpeg "Starting new cluster" error

  9 novembre 2016, par R2-D2

  I want to encode a live stream into webm, but ffmpeg gets stuck in a live lock after 5 seconds stating

  [webm @ 0x1d81940] Starting new cluster at offset 0 bytes, pts 5040dts 5040

  I tried increasing the related AVFormatContext params

  av_opt_set_int(oc->priv_data, "chunk_duration", INT_MAX, 0);
  
  av_opt_set_int(oc->priv_data, "cluster_time_limit", INT_MAX, 0);
  
  av_opt_set_int(oc->priv_data, "cluster_size_limit", INT_MAX, 0);

  which avoids the error for about 30 seconds, but then again ffmpeg hangs

  [webm @ 0xbc9940] Starting new cluster due to timestamp
  
  [webm @ 0xbc9940] Starting new cluster at offset 0 bytes, pts 32800dts 32800

  The error can be reproduced with the official example doc/examples/muxing.c just by writing into a buffer instead of a file like this

  oc = avformat_alloc_context();
  
  oc->oformat = av_guess_format("webm", NULL, NULL);
  
  oc->oformat->flags |= AVFMT_NOFILE;

  and for actual writing

  uint8_t *output_buf;
  
  avio_open_dyn_buf(&oc->pb);
  
  
  
  avformat_write_header(oc, &opt);
  
  /* or */
  
  av_interleaved_write_frame(fmt_ctx, pkt);
  
  
  
  avio_close_dyn_buf(oc->pb, &output_buf);
  
  av_free(output_buf);

  How can I encode webm into a buffer ?
  (And why does it work for files ?)