freshest_frame.py

import threading

class FreshestFrame(threading.Thread):
    running = False

    def __init__(self, capture, name='FreshestFrame'):
        self.capture = capture
        assert self.capture.isOpened()

        self.cond = threading.Condition()
        self.running = False
        self.frame = None
        self.latestnum = 0
        self.callback = None
        
        super().__init__(name=name)
        self.start()

    def start(self):
        self.running = True
        super().start()

    def release(self, timeout=None):
        print('release')
        self.running = False
        self.join(timeout=timeout)
        self.capture.release()

    def run(self):
        counter = 0
        while self.running:
            (rv, img) = self.capture.read()
            if not rv:
                break
            counter += 1

            with self.cond:
                self.frame = img
                self.latestnum = counter
                self.cond.notify_all()

            if self.callback:
                self.callback(img)

    def read(self, wait=True, seqnumber=None, timeout=None):
        with self.cond:
            if wait:
                if seqnumber is None:
                    seqnumber = self.latestnum + 1
                if seqnumber < 1:
                    seqnumber = 1
                
                rv = self.cond.wait_for(lambda: self.latestnum >= seqnumber, timeout=timeout)
                if not rv:
                    return (self.latestnum, self.frame)

            return (self.latestnum, self.frame)