title: php ffmpeg exec & shell_exec process stops after few seconds
body: <p>I'm using PHP script file with simple html interface to control FFMPEG process start and stop from the browser , the script goal is start live streaming on my server that usually runs for hours without stop (using ffmpeg and nginx-rtmp )
   my script were working perfectly until I notice recently This is strange behaviors 
  here is my php script variables </p>
  
  <pre><code>$cast =" /usr/sbin/ffmpeg -loglevel 0 -thread_queue_size 32768 -re -i '".$src."' -i /var/www/example/logo.png -r 23.976 -strict -2 480x360 -aspect 16:9 -filter_complex 'overlay=x=(main_w-overlay_w)/2:y=(main_h-overlay_h)-23' -vcodec libx264 -x264opts colormatrix=bt709 -profile:v high444 4 -b:v 290k -maxrate 290k -bufsize 250k  -af "aresample=async=1:min_hard_comp=0.100000:first_pts=0" -acodec libfdk_aac -profile:a aac_he_v2 -b:a 16k -map_metadata -1 -f flv  rtmp://localhost/hls/live 2&gt;/dev/null &gt;/dev/null  &amp; " ; 
  $output =  shell_exec( $cast   )    ;
  </code></pre>
  
  <p>It's like FFMPEG process continue until original php process ( that call it ) die , at first I thought this issue with the sorce or ffmpeg command but I test the same command on the sell and it works perfectly .
  My suspicion are with on STDIO etc were not  redirected right . even when I excute the same php script from the shell it's do the same stops after few seconds .</p>
  
  <p>=Edit=</p>
  
  <p>Even when I tried to run <code>ffmpeg</code> from the command line and make it run  on the background , I got same behavior the process stop after few seconds , ffmpeg continue running only if I wait for it output .</p>
  
  <p>Here my OS details :-</p>
  
  <pre><code>DISTRIB_DESCRIPTION="Ubuntu 18.04.3 LTS"
  NAME="Ubuntu"
  VERSION="18.04.3 LTS (Bionic Beaver)"
  </code></pre>