Python OpenCV application running very slowly

Question

I am trying to make a simple Video player with OpenCV as a beginner project. I tried on both, an I5 processor and an I9 processor, but the Python script runs very slowly.

Questions:

1. How to increase speed?

2. How to maintain FPS?

   if fileformat in VIDEO_FORMATS:
   cap = cv2.VideoCapture(filepath)
   fps = 24
   backward_seconds = 5
   forward_seconds = 5
   length = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
   
   i = 0
   isPaused = False
   
   def reshape_img(image):
       return cv2.resize(image, (1280, 1024), interpolation=cv2.INTER_AREA)
   
   while True:
       time.sleep(1/fps)
       cap.set(cv2.CAP_PROP_POS_FRAMES, i)
       ret, frame = cap.read()
       frame = reshape_img(frame)
       cv2.imshow('i', frame)
       x = cv2.waitKeyEx(24)
   
       if x == ord("a"):
           if i > backward_seconds * fps:
               i -= backward_seconds * fps
           else:
               i = 0
   
       elif x == ord("d"):
           if i < length - forward_seconds * fps:
               i += forward_seconds * fps
           else:
               i = length - 1
   
       elif x == 32:
           if isPaused == False:
               isPaused = True
   
           elif isPaused == True:
               isPaused = False
   
       elif x == 27:
           break
   
       if not isPaused:
           i += 1
   
   cv2.destroyAllWindows()
   

I don't have much knowledge of how to use OpenCV. So I don't know the things which I am doing wrong.

Answer 1

In order to maintain the FPS, instead of using time.sleep(1 / fps), which would actually result in a lower FPS due to the other parts of the program within the while loop that also takes time, you can define a time delta variable. Here is a minial example:

import time

fps = 24

delta = 1 / fps
last_time = time.time()
new_time = time.time()

while True:
    new_time = time.time()
    if new_time - last_time < delta:
        continue
    last_time += delta
    # Your code here

Adding it to your program's while loop would be:

import time

delta = 1 / fps
last_time = time.time()
new_time = time.time()

while True:
    new_time = time.time()
    if new_time - last_time < delta:
        continue
    last_time += delta
    
    cap.set(cv2.CAP_PROP_POS_FRAMES, i)
    ret, frame = cap.read()
    frame = reshape_img(frame)
    cv2.imshow('i', frame)
    x = cv2.waitKeyEx(24)

    if x == ord("a"):
        if i > backward_seconds * fps:
            i -= backward_seconds * fps
        else:
            i = 0

    elif x == ord("d"):
        if i < length - forward_seconds * fps:
            i += forward_seconds * fps
        else:
            i = length - 1

    elif x == 32:
        if isPaused == False:
            isPaused = True

        elif isPaused == True:
            isPaused = False

    elif x == 27:
        break

    if not isPaused:
        i += 1