title: Create rtsp stream based on opencv images in python
body: <p>My goal is to read frames from an rtsp server, do some opencv manipulation, and write the manipulated frames to a new rtsp server.</p>
  <p>I tried the following based on <a href="https://stackoverflow.com/questions/45544877/write-in-gstreamer-pipeline-from-opencv-in-python/45780731#45780731">Write in Gstreamer pipeline from opencv in python</a>, but I was unable to figure out what the appropriate gst-launch-1.0 arguments should be to create the rtsp server. Can anyone assist with proper arguments to gst-launch-1.0? The ones I tried got stuck in &quot;Pipeline is PREROLLING&quot;</p>
  <pre><code>import cv2
  
  cap = cv2.VideoCapture(&quot;rtsp://....&quot;)
  
  framerate = 25.0
  
  out = cv2.VideoWriter('appsrc ! videoconvert ! '
    'x264enc noise-reduction=10000 speed-preset=ultrafast 
     tune=zerolatency ! '
    'rtph264pay config-interval=1 pt=96 !'
    'tcpserversink host=192.168.1.27 port=5000 sync=false',
    0, framerate, (640, 480))
  
  
  counter = 0
  while cap.isOpened():
    ret, frame = cap.read()
    if ret:
      out.write(frame)
  
      if cv2.waitKey(1) &amp; 0xFF == ord('q'):
        break
    else:
      break
  
  cap.release()
  out.release()
  </code></pre>
  <p>I also tried another solution based on <a href="https://stackoverflow.com/questions/47396372/write-opencv-frames-into-gstreamer-rtsp-server-pipeline">Write opencv frames into gstreamer rtsp server pipeline</a></p>
  <pre><code>import cv2
  import gi 
  
  gi.require_version('Gst', '1.0')
  gi.require_version('GstRtspServer', '1.0') 
  from gi.repository import Gst, GstRtspServer, GObject
  
  class SensorFactory(GstRtspServer.RTSPMediaFactory):
    def __init__(self, **properties): 
      super(SensorFactory, self).__init__(**properties) 
      #self.cap = cv2.VideoCapture(0)
      self.cap = cv2.VideoCapture(&quot;rtsp://....&quot;)
      self.number_frames = 0 
      self.fps = 30
      self.duration = 1 / self.fps * Gst.SECOND  # duration of a frame in nanoseconds 
      self.launch_string = 'appsrc name=source is-live=true block=true format=GST_FORMAT_TIME ' \
                           'caps=video/x-raw,format=BGR,width=640,height=480,framerate={}/1 ' \
                           '! videoconvert ! video/x-raw,format=I420 ' \
                           '! x264enc speed-preset=ultrafast tune=zerolatency ' \
                           '! rtph264pay config-interval=1 name=pay0 pt=96'.format(self.fps)
    
    def on_need_data(self, src, lenght):
      if self.cap.isOpened():
        ret, frame = self.cap.read()
        if ret:
          data = frame.tostring() 
          buf = Gst.Buffer.new_allocate(None, len(data), None)
          buf.fill(0, data)
          buf.duration = self.duration
          timestamp = self.number_frames * self.duration
          buf.pts = buf.dts = int(timestamp)
          buf.offset = timestamp
          self.number_frames += 1
          retval = src.emit('push-buffer', buf) 
          
          print('pushed buffer, frame {}, duration {} ns, durations {} s'.format(self.number_frames, self.duration, self.duration / Gst.SECOND)) 
  
          if retval != Gst.FlowReturn.OK: 
            print(retval) 
  
    def do_create_element(self, url): 
      return Gst.parse_launch(self.launch_string) 
  
    def do_configure(self, rtsp_media): 
      self.number_frames = 0 
      appsrc = rtsp_media.get_element().get_child_by_name('source') 
      appsrc.connect('need-data', self.on_need_data) 
  
  
  class GstServer(GstRtspServer.RTSPServer): 
    def __init__(self, **properties): 
      super(GstServer, self).__init__(**properties) 
      self.factory = SensorFactory() 
      self.factory.set_shared(True) 
      self.get_mount_points().add_factory(&quot;/test&quot;, self.factory) 
      self.attach(None) 
  
  
  GObject.threads_init() 
  Gst.init(None) 
  
  server = GstServer() 
  
  loop = GObject.MainLoop() 
  loop.run()
  </code></pre>
  <p>This solution generates the rtsp server and streams it to it. I can open the resulting rtsp stream in VLC, but it keeps displaying the first frame and does not update with new frames. Anyone who knows why?</p>
  <p>I'm looking for any solution which will enable me with low latency to read frames from an rtsp server into an opencv format, manipulate the frames and output the frames into a new rtsp server (which I also need to create). If something better exists, the solution does not need to be based on gstreamer.</p>
  <p>I am using Ubuntu 16.04 with python2.7 and opencv 3.4.1</p>