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• How to programmatically start/stop FFMPEG stream transcoding

  10 décembre 2019, par Paul Wieland

  I have an ip webcam which provides an MJPEG stream. I can successfully transcode and save that stream with ffmpeg under OSX. The following gives me pretty much what I want :

  ffmpeg -f mjpeg -i "http://user:pass@10.0.1.200/nphMotionJpeg?Resolution=640x480&Quality=Standard" -b:v 1500k -vcodec libx264 /tmp/test.mp4

  That will start an FFMPEG session and begin saving the live stream to my test.mp4 file. pressing q will quit ffmpeg and save the file.

  I would like to programmatically start & stop the recording using a PHP or Bash shell script. I have tried the following :

  <?php
  
  
  
  $pid = pcntl_fork();
  
  
  
  if($pid == -1){
  
      die("could not fork"); 
  
  }elseif($pid){
  
      // we are the parent...
  
      print $pid.' started recording. waiting 10 seconds...';
  
      sleep(10); // Wait 10 seconds
  
  
  
      print_r(shell_exec("kill ".$pid)); // Kill the child recording process
  
  
  
      echo 'done';
  
      exit(); 
  
  }else{
  
      // we are the child process. call ffmpeg.
  
      exec('../lib/ffmpeg -f mjpeg -i "http://user:pass@10.0.1.200/nphMotionJpeg?Resolution=640x480&Quality=Standard" -b:v 1500k -vcodec libx264 /tmp/test.mp4');
  
  }

  But there are two problems :

  1. The ffmpeg process does not end/die (probably because its forked again)
  2. When I manually kill the ffmpeg process, the video file is not readable

• ffplay does not exit in forked child

  6 septembre 2019, par user12030145

  ffplay  -autoexit does not exit in a forked child

  I need to pipe my application (stdout) to ffplay (stdin). I do this by forking ffplay as a child and using -i pipe:0 as argument.

  #include 
  
  #include 
  
  #include <sys></sys>types.h>
  
  #include <sys></sys>wait.h>
  
  
  
  int main(int argc, const char** argv)
  
  {
  
  int tube[2];
  
  int c;
  
  FILE* f = fopen(argv[1], "rb");
  
  pid_t pid;
  
  if (argc &lt; 2) return -1;
  
  if (pipe(tube))  {
  
      perror("Pipe");
  
      return -1;
  
    }
  
  
  
  // main process cats a .mlp file to stdout, sent to a child ffplay stdin through a pipe
  
  char* const arg[] = {"-i", "pipe:0", "-f", "mlp", "-nodisp", "-autoexit", NULL};
  
  switch (pid = fork())    {
  
              case -1:
  
                  fprintf(stderr,"%s\n", "Could not launch ffplay");
  
                  break;
  
  
  
              case 0:
  
                  close(tube[1]);
  
                  dup2(tube[0], STDIN_FILENO);
  
                  execv("/usr/bin/ffplay", arg);
  
                  fprintf(stderr, "%s\n", "Runtime failure in ffplay child process");
  
                  return -2;
  
  
  
              default:
  
                  close(tube[0]);
  
                  dup2(tube[1], STDOUT_FILENO);
  
          }
  
  
  
  // Here the main process code sending the .mlp file to stdout...
  
  
  
  while ((c = fgetc(f)) != EOF) putchar(c);
  
  
  
  waitpid(pid, NULL, 0);
  
  fclose(f);
  
  
  
  // main never returns
  
  return 0;
  
  }

  The issue is that in this context, ffplay -autoexit never exits (GNU-Linux platform). In a main process, ffplay -autoexit always exits at the end of a media file.
  Is there a pure C workaround without using system, popen or scripting ?
  Is this a feature or a bug of ffplay (I cannot tell) ?

• FFMPEG filter using named pipe for I/O to a forked program and legal consideration [closed]

  17 septembre 2021, par alexbuisson

  I would like to develop a ffmpeg filter to have an easier and better integration of the ffmpeg functionalities in case of complex command lines.

  



  Imagine an ffmpeg command line in which you can configure a filter that will use to configure a 3rd party executable to fork and use named pipe to pass video through that external tools.

  



  Technically I can write it, but the question is, is it legal from FFMPEG license point of view (FFMPEG can be GPL or LGPL depending of how it has been built). As far as I understand, if I have an executable called "my_video_transformation.exe" (no relationship with ffmpeg, it just read input pipe and write to output pipe)

  



  It's ok for a user to run the following :

  



  


  (FFMPEG GPL or LGPL).exe decoding_args | my_video_transformation.exe | (FFMPEG GPL or LGPL).exe encoding_args

  


  



  But it's not ok if a user can run something similar to :

  



  


  (FFMPEG GPL or LGPL).exe filter="my_video_transformation.exe" transcoding_args

  


  



  from my understanding of https://www.gnu.org/licenses/gpl-faq.html#GPLPlugins

  



  As soon as you write in a GPL or LGPL executable something that can fork and communicate with 3rd party and by the way maybe a commercial executable, it doesn't respect the license ?

  



  Maybe not the correct place to ask, but would like to have some feedback before starting that project. FFMPEG dev community will reject my code proposal if it's not legal or even border line.

  



  Regards