Error when roslaunch a package:

edit

I am new with ROS and I am not very familiar with python. I am trying to execute roslaunch with this opencv_object_tracking package:

# import all the related packages
import rospy
import argparse
import roslib
import sys
import imutils
import time
import cv2
from imutils.video import VideoStream
from imutils.video import FPS



rospy.init_node('opencv_object_tracking')
rospy.set_param('opencv')
rospy.get_param('opencv')


        # Extract the OpenCV version info
        #(major, minor) = cv2.__version__.split(".")[:2]

        OPENCV_OBJECT_TRACKERS = {"mosse": cv2.TrackerMOSSE_create
                                  }


        #grab the appropriate object tracker
        tracker = OPENCV_OBJECT_TRACKERS[args["tracker"]]()

        # initialize the bounding box coordinates
        initBB = None

        # if grab the reference to the web cam
            print("[INFO] starting video stream...")
            vs = VideoStream(src=0).start()
            time.sleep(1.0)



        # initialize the FPS throughput estimator
        fps = None

        # loop over frames from the video stream
        while True:
        # grab the current frame, then handle if we are using VideoStream
        frame = vs.read()
        frame = frame[1]

        # check to see if we have reached the end of the stream
        if frame is None:
                break

        # resize the frame (so we can process it faster) and grab the
        # frame dimensions
        frame = imutils.resize(frame, width=700)
        (H, W) = frame.shape[:2]

        # check to see if we are currently tracking an object
        if initBB is not None:
        # grab the new bounding box coordinates of the object
        (success, box) = tracker.update(frame)

        # check to see if the tracking was a success
            if success:
                (x, y, w, h) = [int(v) for v in box]
                cv2.rectangle(frame, (x, y), (x + w, y + h),
                (0, 255, 0), 2)

        # update the FPS counter
            fps.update()
            fps.stop()

        # initialize the set of information we'll be displaying on
        # the frame
            info = [
            ("Tracker", args["tracker"]),
            ("Success", "Yes" if success else "No"),
            ("FPS", "{:.2f}".format(fps.fps())),
        ]

        # loop over the info tuples and draw them on our frame
            for (i, (k, v)) in enumerate(info):
            text = "{}: {}".format(k, v)
            cv2.putText(frame, text, (10, H - ((i * 20) + 20)),
                cv2.FONT_HERSHEY_SIMPLEX, 0.6, (0, 0, 255), 2)

        # show the output frame
        cv2.imshow("Frame", frame)
        key = cv2.waitKey(1) & 0xFF

        # if the 's' key is selected, we are going to "select" a bounding
        # box to track
        if key == ord("s"):
        # make sure you press ENTER or SPACE after selecting the ROI)
            initBB = cv2.selectROI("Frame", frame, fromCenter=False,
                showCrosshair=True)

        # start OpenCV object tracker using the supplied bounding box
        # coordinates, then start the FPS throughput estimator as well
            tracker.init(frame, initBB)
            fps = FPS().start()

        # if the `q` key was pressed, break from the loop
        elif key == ord("q"):
                break

        # if we are using a webcam, release the pointer
        if not args.get("video", False):
        vs.stop()

        # otherwise, release the file pointer
        else:
        vs.release()

        rospy.spin()

        # close all windows
        cv2.destroyAllWindows()

And this is the roslaunch that I have made (start.launch):

<launch>
    <node pkg="opencv_object_tracking" type="opencv_object_tracking.py" name="opencv_object_tracking" output="screen">
    <param name="opencv" value="True"/>
    </node>
</launch>

can anyone help me to troubleshoot this?

The error is:

process[opencv_object_tracking-1]: started with pid ... (more)