title: Python 3 generating MP4 files via MP4Box
body: <p>I overhauled my code to use popen and still not getting a new MP4 file.</p>
  
  <p>If I manually type it out in terminal MP4Box works. </p>
  
  <p>But when I run the code below it doesn't raise any error whatsoever. So I am puzzled as what is not working.</p>
  
  <p>The two definition are for tkinter GUI buttons.</p>
  
  <pre><code>global now
  
  #put widgets here
  
  def picapture():
      try:
              global now
              debugLog.insert(0.0, "Date Initialization Done\n")
              now = datetime.datetime.now().strftime("%F_%X")
              debugLog.insert(0.0, now + "\n")
              camera.start_preview(fullscreen=False,window = (200,0,1100,640))
              camera.start_recording('/home/pi/' + now + '.h264')
      except:
              print(traceback.format_exc(limit=10))
  
  def stopcapture():
      try:
              global now
              camera.stop_recording()
              camera.stop_preview()
              MP4Box_Command = ['MP4Box', '-add', now + '.h264', '-0', now + '.mp4']
              convert = subprocess.Popen(MP4Box_Command, stdout=PIPE, bufsize=1, universal_newlines=True)
      except subprocess.CalledProcessError as e:
              raise RunTimeError("Commmand '{}'return with error (code {}): {}".format(e.cmd,e.returncode,e.output))
      except:
              print(traceback.format_exc(limit=10))
  </code></pre>