如何使用OpenCV VideoWriter根据触发器开始和停止保存视频帧

import cv2
import numpy as np

fourcc = cv2.VideoWriter_fourcc(*'XVID')  # 视频编解码器
output_path = 'output.avi'  # 视频保存路径

frame_width = 640  # 视频帧宽度
frame_height = 480  # 视频帧高度
frame_rate = 30.0  # 视频帧率

out = cv2.VideoWriter(output_path, fourcc, frame_rate, (frame_width, frame_height))

is_recording = False  # 触发器状态，初始为False

cap = cv2.VideoCapture(0)  # 打开摄像头
while True:
    ret, frame = cap.read()  # 读取视频帧
    if not ret:
        break
    
    cv2.imshow('Frame', frame)  # 显示视频帧
    
    key = cv2.waitKey(1) & 0xFF
    if key == ord('s'):  # 按下's'键开始保存视频帧
        is_recording = True
    elif key == ord('q'):  # 按下'q'键停止保存视频帧并退出循环
        break
    
    if is_recording:
        out.write(frame)  # 保存视频帧

cap.release()  # 释放摄像头
out.release()  # 释放VideoWriter对象
cv2.destroyAllWindows()  # 关闭所有窗口