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• running ffmpeg from Popen inside (twisted) timer.LoopingCall() stalls

  14 février 2014, par user1913115

  I have an RTSP stream which i need to re-stream as HLS. When RTSP stream goes down (e.g. camera disconnects) I put a blue screen to let the user know that the camera went offline. HLS segmenter is running separately, listening on port 22200 for incoming packets.

  in python the code essentially boils down to this :

  import psutil, subprocess as sb
  
  from twisted.internet import reactor, task
  
  from cameraControls import camStatus, camURL
  
  ffOn = False
  
  psRef = False
  
  def monitor():
  
   print "TIMER TICK"
  
   if camStatus()=='ON' and not ffOn: #camera just came online
  
    cmd = ["ffmpeg", "-i", camURL, "-codec", "copy", "-f", "mpegts", "udp://127.0.0.1:22200"]
  
    ps = sb.Popen(cmd,stderr=sb.PIPE)
  
    psRef=ps
  
   #check the stream:
  
   psmon = psutil.Process(psRef.pid)
  
   if psmon.status!=psutil.STATUS_RUNNING: 
  
    print "FFMPEG STOPPED"
  
  
  
  tmr = task.LoopingCall(monitor)
  
  tmr.start(2)
  
  reactor.run()

  it works fine for 5-6 minutes, then i see the video stall and if i check the cpu usage of the ffmpeg it shows 0, the ffmpeg output doesn't change, as if paused. however psmon.status shows as running, and the timer is still going (i see "TIMER TICK" message pop up every 2 seconds in the command line.

  if i simply run the ffmpeg command from the command line (not from python) then it works for hours no problem.

  does anybody know if the twisted reactor is stalling the process ? or is it the subprocess.Popen itself issue ? or the timer itself is glitching somehow(even though it gets to the 'monitor' function) ? i have other timers running also in the same reactor (same thread), could that be an issue ?

• How does record functionality in vlc works [on hold]

  14 décembre 2013, par quartz

  I am curious about how does "record" functionality of vlc works.
  1) Does it work like screen capture software like "recordmydesktop" ?
  or
  2) Does it save in-memory the frames and latter combine it with tools like ffmpeg ?
  or
  3) Does it simply copy the required information from original video to new video file ?

  Or something else ?

  I want to know these informations because I am developing some simulation tool using a rendering engine. I want my render output to be stored directly in a video file rather than displayed on monitor. If I know these informations, I think it will help.

  Just give me hints, I don't need complete answer.
  This question is not too broad, since I asked specifically about record functionality of vlc media player.

• Bash Scripting FFMPEG how to wait the process to complete

  9 décembre 2013, par user1738671

  I have a strange problem. I have a folder monitor with incrontab that launches an automatic transcoding script on CLOSE_WRITE state of a file I dropped in. The problem is that the script doesn't wait until the ffmpeg process finishes before continuing with the rest of the script commands. This means that the original file get deleted before the transcoding is finished, which is bad.

  First question :
  What is the root cause of this behaviour ?

  Second question : In a bash script, what is the best way to make sure an ffmpeg process is done before get going with the rest of the script ?

  Script :

  #/bin/bash
  
  
  
  #transcoding
  
  /usr/bin/ffmpeg -i "sourcefile push with incron as $1" -vcodec somecode -acodec somecodec "destination file"
  
  
  
  #delete source
  
  rm "path/to/file$1"

  Should I encapsulate my FFMPEG in a while statement ?