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• Swapping FFMPEG input source

  21 novembre 2017, par stevendesu

  I’m using FFMPEG to stream RMTP to a server. I wish to change what I’m streaming without breaking the connection to this server.

  My current FFMPEG command looks like so :

  ffmpeg -f v4l2 -s 1280x720 -r 10 -i /dev/video0 -c:v libx264 -f flv -r 30 -pix_fmt yuv420p "rtmp://server live=true pubUser=user pubPasswd=pass playpath=stream"

  If I wanted to change from /dev/video0 to /dev/video1 then I need to stop this program and re-run the command swapping out the -i bit.

  Since FFMPEG can read from stdin as well as files, I believe it should be possible to switch the input source on the fly by either piping the output of a different program, or utilizing UNIX sockets. There may also be a solution built into FFMPEG which I’m not aware of.

  My question now is : what’s the simplest / least code / most recommended way of switching these inputs ? Is there a third-party tool that’s recommended ? Does FFMPEG have an alternate command-line parameter I’ve never heard of ? If I do use a UNIX socket of stdin, is there a recommended way to change what’s being written to them ?

  One of my concerns is that if I have FFMPEG read in from a UNIX socket and in a separate shell I have a different instance of FFMPEG writing to this UNIX socket, during the brief period when I’m switching sources the first instance of FFMPEG (which is doing the broadcasting) would die, as it couldn’t find any video data to stream.

• 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 ?

• 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 ?