mmal: mmal_vc_port_enable: failed to enable port vc.null_sink:in:0(OPQV): ENOSPC
mmal: mmal_port_enable: failed to enable connected port (vc.null_sink:in:0(OPQV))0x1937060 (ENOSPC)
mmal: mmal_connection_enable: output port couldn't be enabled
Traceback (most recent call last):
File "/home/pi/pi-camera-stream-flask/main.py", line 12, in
pi_camera = VideoCamera(flip=False) # flip pi camera if upside down.
File "/home/pi/pi-camera-stream-flask/camera.py", line 13, in init
self.vs = PiVideoStream().start()
File "/usr/local/lib/python3.7/dist-packages/imutils/video/pivideostream.py", line 10, in init
self.camera = PiCamera()
File "/usr/lib/python3/dist-packages/picamera/camera.py", line 433, in init
self._init_preview()
File "/usr/lib/python3/dist-packages/picamera/camera.py", line 513, in _init_preview
self, self._camera.outputs[self.CAMERA_PREVIEW_PORT])
File "/usr/lib/python3/dist-packages/picamera/renderers.py", line 558, in init
self.renderer.inputs[0].connect(source).enable()
File "/usr/lib/python3/dist-packages/picamera/mmalobj.py", line 2212, in enable
prefix="Failed to enable connection")
File "/usr/lib/python3/dist-packages/picamera/exc.py", line 184, in mmal_check
raise PiCameraMMALError(status, prefix)
picamera.exc.PiCameraMMALError: Failed to enable connection: Out of resources
Exception ignored in: <function VideoCamera.del at 0xac399228>
Traceback (most recent call last):
File "/home/pi/pi-camera-stream-flask/camera.py", line 18, in del
self.vs.stop()
AttributeError: 'VideoCamera' object has no attribute 'vs'

Please help.