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• Error -138 returns "Error number -138 occurred"

  29 avril 2016, par bot1131357

  I am trying to create a program that listens for a period of time, and then times out so that it can return to work on other tasks and retry again later. Here is the code I am testing with :

  AVFormatContext *pFormatCtx = NULL;
  
  AVCodecContext *codecCtx = NULL;
  
  AVCodec *codec;
  
  int ret = 0;
  
  
  
  // Register all formats and codecs
  
  av_register_all();
  
  avformat_network_init(); // for network streaming
  
  
  
  AVDictionary *d = NULL;           // "create" an empty dictionary
  
  av_dict_set(&d, "timeout", "5", 0); // add an entry
  
  av_dict_set(&d, "rtsp_flags", "listen", 0); // add an entry
  
  
  
  char filename[100];
  
  sprintf_s(filename, sizeof(filename), "%s", "rtsp://127.0.0.1:8554/demo");
  
  
  
  
  
  //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  
  printf_s("Open video file.\n");
  
  // Open video file
  
  ret = avformat_open_input(&pFormatCtx, filename, NULL, &d);   // Returns -138 here 
  
  if (ret <0)
  
  {
  
      printf_s("Failed: cannot open input.\n");
  
      av_strerror(ret, errbuf, ERRBUFFLEN);
  
      fprintf(stderr, "avformat_open_input() fail: %s\n", errbuf);
  
      continue;
  
      //return -1; // Couldn't find stream information
  
  }

  In the listening mode, avformat_open_input() returns -138. Using av_strerror() gives the following explanation : "Error number -138 occurred"

  Is this an Easter egg ? What does -138 stand for ?

• Why does ffmpeg have bigger latency on dark images ?

  19 novembre 2017, par doodoroma

  I have a c# application to stream real camera images using ffmpeg. The input images are in raw, 8-bit gray-scale format. I created an ffmpeg stream using the standard input to feed the images and send the output packages to websocket clients.

  I start an external ffmpeg process using this config :

  -f rawvideo -pixel_format gray -video_size " + camera.Width.ToString() + "x" + camera.Height.ToString() + " -framerate 25 -i - -f mpeg1video -b:v 512k -s 320x240 -

  Typical image size is 1040*1392 pixels

  I display the stream on the browser, using jsmpeg library

  This works with a reasonable latency ( 500ms on localhost), but when the camera image is really dark (black image), the latency is extremely big ( 2-3 seconds on localhost). When there is something bright on the image again after a black period, it takes 2-3 seconds to "synchronize".

  I was thinking that black images are really easy to compress and will generate really small packages, jsmpeg has almost no information to display and wait until a complete data package arrives, but I couldn’t prove my theory.

  I played with ffmpeg parameters like bitrate and fps but nothing has changed.

  Is there any settings which I could try ?

• FFmpeg drawtext and live coordinates with sendcmd/zmq

  9 mai 2019, par DavidK

  I’d like to use a marker on a live video source which has external live data to set x,y coordinates. sendcmd can read the text file but it won’t update it, so later updates are not executed. Is it possible only with zmq ? And if so, can I use zmq as a single filter (with drawtext), not with filter complex ?

  I have a python that exports live coordinates in the appropriate format to a cmd.txt file. I use unix time for the coordinates and I also copy the input timestamps from the live loopback device so they have almost the same time. There’s a small delay so I have compensated the exported timestamps with +1.5s. This means the marker is moving for this extra period (while timestamps in cmd.txt are a bit ahead of the live source), but it won’t update any more. I assume that FFmpeg reads this cmd.txt and won’t update it any more but my python is writing it continuously.

  Example line of the cmd.txt :

  1557402120.3119707 drawtext reinit 'x=752:y=480';

  This is the actual ffmpeg pipe :

  ffmpeg -fflags nobuffer -vaapi_device /dev/dri/renderD128 -f v4l2 -i /dev/video0 -vf "sendcmd=f=cmd.txt,drawtext=fontfile=font.ttf:fontsize=30:fontcolor=white:r=25:text='o',format=nv12,hwupload" -copyts -c:v h264_vaapi -qp 24 -y 0.mp4

  Source is a loopback device with unix time as input timestamp.