cv2 VideoCapture 在启动时挂起 flask 服务器

Question

Flask server hangs at startup (and doesn't serve any page). This happens because is trying to initialize OpenCV VideoCapture inside a class:

I have a LaptopCamera class that initializes the laptop camera using OpenCV:

class LaptopCamera:
    def __init__(self):
        self.video = cv2.VideoCapture(0)
        self.video.set(cv2.CAP_PROP_FRAME_WIDTH, 1920)
        self.video.set(cv2.CAP_PROP_FRAME_HEIGHT, 1080)
        self.video.set(cv2.CAP_PROP_FPS, 60)
        self.video.set(cv2.CAP_PROP_BUFFERSIZE, 1)

    def single_image(self):
        """return jpeg image of frame"""
        ret, jpeg = cv2.imencode('.jpeg', self.read_video())
        return jpeg.tobytes()

and then it is used in the flask server like this:

@API.route('/picture.jpeg')
def provide_jpeg():
    cam.read_video()
    return Response(cam.single_image(), mimetype='image/jpeg')

cam = LaptopCamera()

if __name__ == '__main__':
    tankyAPI.run(HOST, PORT, debug=True)

If I first comment cam = LaptopCamera() , start the server, uncomment the cam = LaptopCamera() and wait for it to reload it works just fine.

I am wondering why does this happen? and how could I find a solution?

Answer 1

I have a similar experience when developing my application. The solution I had was to remove all the libraries, and create a new environment, and re-install all the libraries. It was on Ubuntu 18, and there are some system libraries that are different between the CV2 and other python modules, so the easiest way to solve my problem is to start from scratch and to reinstall every library.

Hope this helps.