Flask script for a video ringbuffer for raspberry pi camera; HTTP trigger to dump the buffer contents (last x seconds) to disk.

cam.py

import subprocess
from flask import Flask
import signal
from time import sleep
from datetime import datetime

vidproc = None

def start():
    cmd = "raspivid -c -o out.h264 -s -t 120000 -fps 30 -rot 180 -w 1920 -h 1080 -b 15000000"
    global vidproc
    vidproc = subprocess.Popen(cmd.split())

def save_vid():
    global vidproc
    vidproc.send_signal(signal.SIGUSR1)
    vidproc.wait()
    cmd = "MP4Box -fps 30 -add out.h264 " + datetime.now().strftime("%Y%m%d-%H%M%S") + '.mp4'
    subprocess.run(cmd.split())
    start()


app = Flask(__name__)

@app.route('/')
def save():
    save_vid()
    return "Hello World!"


if __name__ == '__main__':
    start()
    app.run(host='0.0.0.0')

Requires MP4Box to be installed on the Pi, and flask be installed for python.
To use, point a browser or GET request to the Pi's IP address, port 5000 e.g. http://192.168.4.9:5000/