Get the current frame from USB camera using opencv - python-3.x

Question

I'm using opencv's VideoCapture() to read frames from a USB camera. What I want is getting still images at some random time.
What I have now is that I initialize the cap using:
cap = cv2.VideoCapture(0)
cap.set(3, 640)
cap.set(4, 480)
Then use this bit of code to get frame:
ret, frame = cap.read()
I can get the first frame correctly. However, it seems the next time I acquire a frame (after a random time gap), it is not the frame at that time, but the consecutive frame next to the first one (almost the same as the first frame).
I also tried to release the cap after the first time and get a new cap for the second capture. But initialing the cap takes around 1 second, which is too long and cannot be accepted.
Is there any solution to this problem?
Thanks.

Answer 1

A solution is to continually capture frames, but only display a frame after a random time gap.
Wait a random number of frames:
import random
import cv2
cap = cv2.VideoCapture(0)
def wait(delay):
framecount = 0
# capture and discard frames while the delay is not over
while framecount < delay:
cap.read()
framecount += 1
while True:
# select and wait random number of delay frames
delay = random.randint(50,150)
wait(delay)
# get and display next frame
ret, img = cap.read()
cv2.imshow("Image", img)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cv2.destroyAllWindows()
Random time wait:
import time
import random
import cv2
curr_time = time.time()
cap = cv2.VideoCapture(0)
def wait(delay):
# capture and discard frames while the delay is not over
while time.time()-curr_time < delay:
cap.read()
while True:
# select and wait random delay time
delay = random.random()
wait(delay)
# update curr_time
curr_time = time.time()
# get and display next frame
ret, img = cap.read()
cv2.imshow("Image", img)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cv2.destroyAllWindows()