Opencv reads webcam video and saves it locally

The code and comments are as follows ：

import cv2
import time


#  Acquisition time 
def get_time():
    it = time.strftime("%Y%m%d%H%M%S", time.localtime())  #  Time without separator   Can be used as file name 
    ft = time.strftime("%Y-%m-%d %H:%M:%S", time.localtime()) #  Time format 
    return [it, ft]

stream = "rtsp://username:password@ip_address/ch1/main/av_stream" #  Hikvision camera address   User name, password 
video_path = '' #  Video storage address 
cap = cv2.VideoCapture(stream) #  Read in video 
#  Get high   wide   Frame rate 
w = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH)) 
h = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
fps = max(cap.get(cv2.CAP_PROP_FPS) % 100, 0) or 25.0

if cap.isOpened() == False or w == 0 or h == 0:
    print("connect failed")

frame_count = 0 #  Record the number of frames 
temp_path = video_path + get_time()[0] + ".mp4" #  Save the path  （ Spell time as the file name ）
#  Writing videos 
vid_writer = cv2.VideoWriter(temp_path, cv2.VideoWriter_fourcc(*'mp4v'), fps, (w, h))
while True:
    cap.grab() #  Get the next frame 
    success, im = cap.retrieve() #  decode 
    if success:
        frame_count += 1 #  Frame number plus 1
    vid_writer.write(im) #  Save video 
    if frame_count > 7500: #  Set a time   How often do you keep 
        vid_writer.release()  #  Save to local 
        frame_count = 0 #  Zero clearing 
        break
    # cv2.imshow("camera", img)
    # cv2.waitKey(1)
cap.release() #  Release resources