Allows to always get most recent frame, in case video capture loop has some (computation) delay inside

BufferlessVideoCapture.py

# Based on: https://stackoverflow.com/questions/43665208/how-to-get-the-latest-frame-from-capture-device-camera-in-opencv/54755738#54755738
#
# Added:
# - configurable delay handling
# - renamed class
# - per frame timestamp output
#
import cv2, threading, time, queue
from sys import argv

wait = 0 if len(argv) == 1 else float(argv[1])

class BufferlessVideoCapture:

  def __init__(self, name):
    self.cap = cv2.VideoCapture(name)
    self.q = queue.Queue()
    t = threading.Thread(target=self._reader)
    t.daemon = True
    t.start()

  # read frames as soon as they are available, keeping only most recent one
  def _reader(self):
    while True:
      ret, frame = self.cap.read()
      if not ret:
        break
      if not self.q.empty():
        try:
          self.q.get_nowait()   # discard previous (unprocessed) frame
        except queue.Empty:
          pass
      self.q.put(frame)

  def read(self):
    return self.q.get()

cap = BufferlessVideoCapture(0)
while True:
  time.sleep(wait)
  print("after wait, before cap.read()", time.time())
  frame = cap.read()

  cv2.imshow("frame", frame)

  if chr(cv2.waitKey(1)&255) == 'q':
    break

Call with "python BufferlessVideoCapture.py 2" for 2 second delay between loop executions.
Whenever a timestamp message is written, do after a seond a change (eg. of hand) in view.
When next timestamp gets printed, newly displayed frame will show changed scene.