title: how to make a queue in php with mysql
body: <p>hy,</p>
  
  <p>in my script i run a exec() function to make a movie file with ffmpeg.</p>
  
  <p>the problem is ffmpeg can run only 1 time on the server,</p>
  
  <p>if 2 people are online on server and first one already run ffmpeg i want the second to wait until the first end the process</p>
  
  <p>how to code this?</p>
  
  <p>thank  you</p>