How to use the vidgear.gears.CamGear function in vidgear

image_resolution = ast.literal_eval(image_resolution)
    has_display = 'DISPLAY' in os.environ.keys() or sys.platform == 'win32'
    video_writer = None

    if filename is not None:
        rotation_code = check_video_rotation(filename)
        video = cv2.VideoCapture(filename)
        assert video.isOpened()
    else:
        rotation_code = None
        if disable_vidgear:
            video = cv2.VideoCapture(camera_id)
            assert video.isOpened()
        else:
            video = CamGear(camera_id).start()

    model = SimpleHRNet(
        hrnet_c,
        hrnet_j,
        hrnet_weights,
        resolution=image_resolution,
        multiperson=not single_person,
        max_batch_size=max_batch_size,
        device=device
    )

    while True:
        t = time.time()

        if filename is not None or disable_vidgear:
            ret, frame = video.read()