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• Evolution #2370 : Activation d’une pétition et autres options relativement rares

  21 février 2019, par tcharlss (*´_ゝ｀)

  À lier au ticket #4180
  PR fait : https://git.spip.net/dist/petitions/pulls/1

• Accurate FFmpeg capture start time

  28 juillet 2016, par Adam

  I’m using ffmpeg from the command line to capture from a webcam to a file using the following :

  ffmpeg -y -rtbufsize 702000k -f dshow -s 320x240 -r 25 -i video="<device>" -t 10 -vcodec mjpeg -q:v 2 out.mp4
  
  </device>

  There is a slight delay between executing the command and the start of the capture ( 0.5 sec).
  I’m trying to find a way to accurately determine the start time (UTC/GMT) of the capture.

  My initial thought was to use the file-creation time as this might accurately reflect when the first frame was encoded (as opposed to when the command was executed). Unfortunately the file creation time is only accurate to the second which is not precise enough (and I’m not sure this would have given an accurate result anyway).

  My next thought was to use ffmpegs timestamp option. According to the documentation (http://www.ffmpeg.org/ffmpeg.html) :

  ‘-timestamp time (output)’

  Set the recording timestamp in the container. The syntax for time is:
  
  
  
  now|([(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH:MM:SS[.m...])|(HHMMSS[.m...]))[Z|z])

  If the value is "now" it takes the current time. Time is local time unless ’Z’ or
  ’z’ is appended, in which case it is interpreted as UTC. If the year-month-day part
  is not specified it takes the current year-month-day.

  So I added the option :

  ffmpeg -y -rtbufsize 702000k -f dshow -s 320x240 -r 25 -i video="<device>" -t 10 -vcodec mjpeg -q:v 2 -timestamp now out.mp4
  
  </device>

  Unfortunately ffmpeg doesn’t seem to like this :

  Option timestamp (set the recording timestamp (’now’ to set the
  current time)) cannot be applied to output file out.mp4 — you are
  trying to apply an input option to an output file or vice versa. Move
  this option before the file it belongs to.

  Error parsing options for output file out.mp4.

  Error opening output files : Error number -22 occurred

  The documentation says -timestamp is an output option and it appears to be applied to the output file so I’m confused by this error.

  Can anyone suggest a way to accurately determine the capture start time ?

  Does anyone know why the -timestamp option gives an error ?

• How to programmatically start/stop FFMPEG stream transcoding

  3 février 2014, 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