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• How to detect blue screen of ffmpeg video packet ?

  28 novembre 2017, par 심상원

  Good morning. There is one question about FFMPEG.

  I’m using FFMPEG to study C ++ on Linux.

  When the camera spirituality is RTSP and the format is H.264,

  I would like to determine if the camera image is a blue screen, but the following concepts are confusing.

  1. KeyFrame comes in 1 second or every X seconds cycle. Does the KeyFrame get delivered from the camera even if it is still the same image ?

  2. If the KeyFrame is delivered, is the size of the packet transmitted between the cycles zero ?

  3. If the above method is the same as normal image, should I compare the individual frames after decoding ?

  If you do not have any of these questions, please let me know if you have a good way.

  Thank you.

• remuxing audio and videos (screen and presenter) captured at the same time does not synchronize

  22 septembre 2014, par user28163

  trying to merge a screencast with a video (without sound) and a sound steam which has been captured separately using ffmpeg using a bash command. All the stream-capture were started at the same time and all ffmpeg processes killed at the same time (pkill). But when I remux them together, the screencast and video does not match, and thus sound does not synchronize either.

  Where did I go wrong ? Any inputs appreciated from ffmpeg experts here. Thanks in advance.

  Please find the ffmpeg output as follows :

  1. The ffmpeg log of two videos muxing (http://pastebin.com/XwnDSf5i)
  2. The ffmpeg log of remuxing the sound with the side-by side video as of 1 above (cannot paste as the pastebin limit exeeded :( ).

  UPDATE :

  After checking the lenght of the screencast, I figured out that the screen capture (though started and stopped at the same time as video and sound using a bash script), is shorter in lenght by 1m54s than video and audio (former 34:22 vs later 36:16). The video was captured in h264 mp4 wrapper at -r 30. So is screen capture but lossless

  %ffmpeg -report -f x11grab -r 30 -s 1920x1080 -i :0.0 -qscale 0 -vcodec libx264 -threads 4 screen.m4v

  Could that be the reason for the delay ? Is there any way to extend the screencast against the videos ? Thanks !

• FFMPEG Green Screen from raw pictures

  21 août 2016, par Mohammad Abu Musa

  I am writing a screen recorder, I get raw data from Chrome and I want to covert it to webm files. I manged successfully to export the videos with the correct periods but the issue that I get a green screen instead of the screen capture. I am not sure what could be wrong.

  Is it writing to file ? or passing the parameters to fwrite function ?

  void EncoderInstance::OnGetFrame(int32_t result, pp::VideoFrame frame) {
  
      if (result != PP_OK)
  
          return;
  
  
  
      const uint8_t* data = static_cast<const>(frame.GetDataBuffer());
  
      pp::Size size;
  
      frame.GetSize(&amp;size);
  
      uint32_t buffersize = frame.GetDataBufferSize();
  
  
  
  
  
      if (is_recording_) {
  
          vpx_codec_iter_t iter = NULL;
  
          const vpx_codec_cx_pkt_t *pkt;
  
          // copy the pixels into our "raw input" container.
  
          int bytes_filled = avpicture_fill(&amp;pic_raw, data, AV_PIX_FMT_YUV420P, out_width, out_height);
  
          if(!bytes_filled) {
  
              Logger::Log("Cannot fill the raw input buffer");
  
              return;
  
          }
  
  
  
          if(vpx_codec_encode(&amp;codec, &amp;raw, frame_cnt, 1, flags, VPX_DL_REALTIME))
  
                die_codec(&amp;codec, "Failed to encode frame");
  
  
  
          while( (pkt = vpx_codec_get_cx_data(&amp;codec, &amp;iter)) ) {
  
              switch(pkt->kind) {
  
                  case VPX_CODEC_CX_FRAME_PKT:
  
                      glb_app_thread.message_loop().PostWork(callback_factory_.NewCallback(&amp;EncoderInstance::write_ivf_frame_header, pkt));
  
                      glb_app_thread.message_loop().PostWork(callback_factory_.NewCallback(&amp;EncoderInstance::WriteFile, pkt));
  
                      break;
  
                  default:break;
  
              }
  
          }
  
  
  
          frame_cnt++;
  
      }
  
  
  
      video_track_.RecycleFrame(frame);
  
      if (need_config_) {
  
          ConfigureTrack();
  
          need_config_ = false;
  
      } else {
  
          video_track_.GetFrame(
  
                  callback_factory_.NewCallbackWithOutput(
  
                          &amp;EncoderInstance::OnGetFrame));
  
      }
  
  }
  
  </const>