多线程提取长视频帧

import threading
import cv2
import time
import os
path2 = '../image/'  #图片保存位置
if not os.path.exists(path2):
    os.makedirs(path2)
class myThread(threading.Thread):
    
    def __init__(self,  start_frame, length):
        super(myThread, self).__init__()
        self.start_frame = start_frame
        self.length = length

    def run(self):
        
        cap = cv2.VideoCapture("E:盐田视频数据\2021-09-27\3号机9月18跑大车\00000001744000000.mp4")  #视频位置
        cap.set(cv2.CAP_PROP_POS_frameS, self.start_frame)
        freq = 100
        for idx in range(self.length):
            ret = cap.grab()
            if not ret:
                break

            if idx % freq == 0:
              ret, frame = cap.retrieve()
              if frame is None:  # exist broken frame
                break
              cv2.imwrite(path2 + str(idx+self.start_frame) + '.jpg', frame)
            # do something else
            ...
        cap.release()


n = 10
a=[1]*n

for i in range(n):
    a[i]=myThread(i*40000,i*40000+40000)  #一个线程处理40000帧数据
    i = i + 1

for i in range(n):
    a[i].start()