records_the_last_X_seconds_of_the_video.py

# pip install opencv-python
import cv2
import queue
import threading
import time

class Video(threading.Thread):
    def __init__(self, camera, interval, path) -> None:
        threading.Thread.__init__(self)
        self._cam = cv2.VideoCapture(camera)

        self.frame_width = int(self._cam.get(cv2.CAP_PROP_FRAME_WIDTH))
        self.frame_height = int(self._cam.get(cv2.CAP_PROP_FRAME_HEIGHT))
        self.size = (self.frame_width, self.frame_height)  
        # set camera resolution
        self._queue_frame = queue.Queue()
        self._queue_timestamp = queue.Queue()
        self._interval = interval
        self.shutdown_flag = threading.Event()
        self._path = path


    def run(self):
        timestamp = time.time()
        while not self.shutdown_flag.is_set():
            ret, frame = self._cam.read()
            timestamp = time.time()
            if ret:
                if self._queue_frame.empty():
                    self._queue_frame.put(frame)
                    self._queue_timestamp.put(timestamp)
                elif timestamp - self._queue_timestamp.queue[0] > self._interval:
                    # remove frame
                    self._queue_frame.get()
                    self._queue_timestamp.get()
                    # put frame
                    self._queue_frame.put(frame)
                    self._queue_timestamp.put(timestamp)
                else:
                    # put frame
                    self._queue_frame.put(frame)
                    self._queue_timestamp.put(time.time())

        
        self._cam.release()
        self.fps = int(self._queue_frame.qsize() / (timestamp - self._queue_timestamp.queue[0]))
        print(self.fps)
        print(self._queue_frame.qsize())
        self.save_video()

    def save_video(self):
        file = cv2.VideoWriter(self._path, cv2.VideoWriter_fourcc(*"mp4v"), self.fps, self.size)

        while not self._queue_frame.empty():
            frame = self._queue_frame.get()
            file.write(frame)

        file.release()

if __name__ == '__main__':
    print("Main")
    video = Video(camera = 0, interval = 30, path = "./test.mp4")
    print("Start")
    video.start()
    print("Started")

    time.sleep(60)
    print("After 60 second")
    video.shutdown_flag.set()
    print("shutdown flag")
    video.join()
    print("After join")