CV2: closing webcam and reopening in different function

Question

In this code I want to display 3 types of classification: "Known", "Unknown" and "Hostile" using open cv and face_recognition. The first function (firtsCase()) contains "Known", "Unknown" and that it's everything ok. What I want to do is: when the program knows that is in the function secondCase() that is "hostile" and I press "q", the webcam must close and launch the function that sends me back to the cases "Known" and "Unknown" (call at the end of secondCase() with firstCase()) to reopen the webcam and reclassify. You can find it in the latest part of function secondCase().

I have this error:

small_frame = cv2.resize(frame, (0, 0), fx=0.25, fy=0.25) cv2.error: OpenCV(4.5.5) /Users/runner/work/opencv-python/opencv-python/opencv/modules/imgproc/src/resize.cpp:4052: error: (-215:Assertion failed) !ssize.empty() in function 'resize'

I know this error shows up because it is trying to resize something that has already been manipulated, but I don't know how can I fix it.

This is the code:

video_capture = cv2.VideoCapture(0)


face2 = face_recognition.load_image_file(os.path.abspath("path2"))
face2_face_encoding = face_recognition.face_encodings(face2)[0]

known_face_encodings = [
    face2_face_encoding
]

known_face_names = [
    "Giulia"
]

face_location = []
face_encodings = []
face_names = []

def firstCase():
    while True:
            ret, frame = video_capture.read()
            small_frame = cv2.resize(frame, (0, 0), fx=0.25, fy=0.25)
            rgb_small_frame = small_frame[:, :, ::-1]
            process_this_frame = True
            face = False
            if process_this_frame:
                face_locations = face_recognition.face_locations(rgb_small_frame)
                face_encodings = face_recognition.face_encodings(rgb_small_frame, face_locations)

                face_names = []
                for face_encoding in face_encodings:
                    matches = face_recognition.compare_faces(known_face_encodings, face_encoding, tolerance=0.6)
                    name = "Sconosciuto"
                    face = True
                    face_distances = face_recognition.face_distance(known_face_encodings, face_encoding)
                    best_match_index = np.argmin(face_distances)
                    if matches[best_match_index]:
                        name = known_face_names[best_match_index]
                        face = False
                        face_distances = face_recognition.face_distance(known_face_encodings, face_encoding)
                        best_match_index = np.argmin(face_distances) 
                    face_names.append(name)
            process_this_frame = not process_this_frame
            if face:
                for (top, right, bottom, left), name in zip(face_locations, face_names):
                    top *= 4
                    right *= 4
                    bottom *= 4
                    left *= 4
                    cv2.rectangle(frame, (left, top), (right, bottom), (40,48,48), 2)
                    cv2.rectangle(frame, (left, bottom - 35), (right, bottom), (40,48,48), cv2.FILLED)
                    font = cv2.FONT_HERSHEY_DUPLEX
                    cv2.putText(frame, name, (left + 6, bottom - 6), font, 0.6, (255, 255, 255), 1)
                cv2.imshow('Video', frame)
            else:
                for (top, right, bottom, left), name in zip(face_locations, face_names):
                    top *= 4
                    right *= 4
                    bottom *= 4
                    left *= 4
                    cv2.rectangle(frame, (left, top), (right, bottom), (0, 255, 0), 2)
                    cv2.rectangle(frame, (left, bottom - 35), (right, bottom), (0, 255, 0), cv2.FILLED)
                    font = cv2.FONT_HERSHEY_DUPLEX
                    cv2.putText(frame, name, (left + 6, bottom - 6), font, 0.6, (255, 255, 255), 1)
                cv2.imshow('Video', frame)    
            if cv2.waitKey(1) & 0xFF == ord('q'):
                break
    video_capture.release()
    cv2.destroyAllWindows()

def secondCase():
    while True:
        ret, frame = video_capture.read()
        small_frame = cv2.resize(frame, (0, 0), fx=0.25, fy=0.25)
        rgb_small_frame = small_frame[:, :, ::-1]
        process_this_frame = True
        face = False
        if process_this_frame:
            face_locations = face_recognition.face_locations(rgb_small_frame)
            face_encodings = face_recognition.face_encodings(rgb_small_frame, face_locations)

            face_names = []
            for face_encoding in face_encodings:
                matches = face_recognition.compare_faces(known_face_encodings, face_encoding, tolerance=0.6)
                name = "Ostile"
                face = True
                face_distances = face_recognition.face_distance(known_face_encodings, face_encoding)
                best_match_index = np.argmin(face_distances)
                if matches[best_match_index]:
                    name = known_face_names[best_match_index]
                    face = False
                face_names.append(name)
        process_this_frame = not process_this_frame
        if face:
            for (top, right, bottom, left), name in zip(face_locations, face_names):
                top *= 4
                right *= 4
                bottom *= 4
                left *= 4
                cv2.rectangle(frame, (left, top), (right, bottom), (0,0,0), 2)
                cv2.rectangle(frame, (left, bottom - 35), (right, bottom), (0,0,0), cv2.FILLED)
                font = cv2.FONT_HERSHEY_DUPLEX
                cv2.putText(frame, name, (left + 6, bottom - 6), font, 0.6, (255, 255, 255), 1)
            cv2.imshow('Video', frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    video_capture.release()
    cv2.destroyAllWindows()
    
    firstCase()
    

print("Inizio scansione :" + time.ctime() + "\nCitofono attivo. Citofona premendo a... ")

sel = selectors.DefaultSelector()
sel.register(sys.stdin, selectors.EVENT_READ)
sys.stdout.flush()
pairs = sel.select(timeout=5)

if pairs:
    if input("Citofona premendo 'a' \n"):
        firstCase()
else:
    secondCase()

Thank you all for helping.