cv2 in a python script not working when called by php

I am facing a problem with the python script when called by PHP.

The python script is working great when I run it from the terminal.

but when I call the python script from PHP it runs half, when statements of the cv2 module come the code does not work

I have imported cv2 module

the python script is

video2frames.py

    # Importing all necessary libraries 
import cv2 
import os 


# Read the video from specified path 
cam = cv2.VideoCapture("input/video.mp4") 

try: 
    
    # creating a folder named data 
    if not os.path.exists('input/frames'): 
        os.makedirs('input/frames') 

# if not created then raise error 
except OSError: 
    print ('Error: Creating directory of frames') 

# frame 
currentframe = 0

print('till before while loop worked')

a = 1
 
while(a<250): 
    # reading from frame 
    print('worked inside while loop')
    ret,frame = cam.read() 
    
    if ret: 
        # if video is still left continue creating images 
        print('worked inside if condition')
        name = './input/frames/frame' + str(currentframe) + '.png'
        print ('Creating...' + name) 
        # writing the extracted images 
        cv2.imwrite(name, frame) 
        # increasing counter so that it will 
        # show how many frames are created 
        currentframe += 1
        print('worked inside if')
    else:
        print('worked inside else');break

# Release all space and windows once done 
cam.release() 
cv2.destroyAllWindows()

the PHP code I used to call the python script is

shell_exec('python3 video2frames.py');