Yolo Spatial detection FPS drop when not visualising output

Hi. I'm having an issue with depthai_sdk. I have task to detect objects using yolo, but what I need is only detections and a frame once per 1s. I use code below to print outputs of the yolo. with code as it is, I achieve 15FPS, but with commenting the 14,15 line, the FPS drops to 2 and no detection is provided. Als setting blocking = False on line 25 leads to failure.

Thank you, Jan

1. def callback(packet: DetectionPacket):
2.     visualizer = packet.visualizer
3.     try:
4.         print()
5.         for inx in range(len(packet.detections)):
6.             print('Detected: ' + packet.detections[inx].label + ' at' + str(packet.detections[inx].centroid()))
7.             print('Spatial: x ' + str(visualizer.objects[0].detections[0].spatialCoordinates.x) + 'mm ,y '
8.                 + str(visualizer.objects[0].detections[inx].spatialCoordinates.y) + 'mm ,z '
9.                 + str(visualizer.objects[0].detections[inx].spatialCoordinates.z) + 'mm.')
10.             print('Confidence: ' + str(visualizer.objects[0].detections[inx].confidence))
11.         print(visualizer.objects[1].text )
12.     except:
13.         pass
14.     frame = visualizer.draw(packet.frame)
15.     cv2.imshow('Visualizer', frame)
16.    
17. with OakCamera(args=args) as oak:
18.     color = oak.create_camera('color')
19.     color.config_color_camera(isp_scale=(1,2))
20.     nn = oak.create_nn(args['config'], color, nn_type='yolo', spatial=True)
21.     for inx in range(len(nn._labels)):
22.         nn._labels[inx] = true_labels[inx]
23.        
24.     oak.visualize(nn.out.passthrough, fps=True, callback=callback)
25.     oak.start(blocking=True)