making a memory only fileobject in python with pyfilesystem

Question

I have written a motion detection/ video program using opencv2 which saves video output for x seconds. if motion in detected during that time, the output is saved as an alternate named file, but if not motion is detected then the file is overwritten. To avoid needless wear on a flash based memory system, I want to write the file to the RAM, and if motion is detected then save it to the non-volatile memory.

I am trying to create this file in the RAM using pyfilesystem-fs.memoryfs

import numpy as np
import cv2, time, os, threading, thread
from Tkinter import *
from fs.memoryfs import MemoryFS

class stuff:

    mem=MemoryFS()
    output = mem.createfile('output.avi')
    rectime=0
    delay=0
    kill=0
    cap = cv2.VideoCapture(0)
    #out = cv2.VideoWriter('C:\motion\\output.avi',cv2.cv.CV_FOURCC('F','M','P','4'), 30, (640,480),True)
    out = cv2.VideoWriter(output, cv2.cv.CV_FOURCC('F','M','P','4'), 30, (640,480),True)

This is the motion detection part

if value > 100:
        print "saving"
        movement=time.time()
        while time.time()<int(movement)+stuff.rectime:
            stuff.out.write(frame)
            ret, frame = stuff.cap.read()


        if stuff.out.isOpened() is True:
            stuff.out.release()
        os.rename(stuff.output, 'c:\motion\\' + time.strftime('%m-%d-%y_%H-%M-%S') + '.avi')

the os.rename function returns TypeError must be string, not None

I'm clearly using memoryfs incorrectly, but cannot find any examples of its use.

EDIT I use the following line to open the file object and write to it

stuff.out.open(stuff.output, cv2.cv.CV_FOURCC(*'FMP4'),24,(640,480),True)

however this returns False , I'm not sure but it appears it can't open the file object.

Is there a reason you don't just use io.BytesIO or cStringIO? — Kevin
– Kevin, Commented Aug 31, 2015 at 23:08
probably because I ran into memoryFS first. Could you give me an example of how to implement this to save the video to the buffer then write the buffer to a file. — jeffpkamp
– jeffpkamp, Commented Aug 31, 2015 at 23:21
Em. Maybe, it isn't clear to you that mem.createfile(...) returns None. Always. Not a file object. — mingaleg
– mingaleg, Commented Aug 31, 2015 at 23:55
@shhdup I thought of that after I looked at it again. I then did f = mem.open('output.avi') but this is an _io.TextWrapperIO type, not a string or unicode type. — jeffpkamp
– jeffpkamp, Commented Sep 1, 2015 at 0:53
Yes, it's file-like object. You could read from it with f.read() — mingaleg
– mingaleg, Commented Sep 1, 2015 at 1:12

mingaleg · Accepted Answer · 2015-08-31 23:32:28Z

1

To move your file form MemoryFS to real file system, you should read orig file and write it to dest file, something like

with mem.open('output.avi', 'b') as orig:
    with open('c:\\motion\\' + time.strftime('%m-%d-%y_%H-%M-%S') + '.avi')) as dest:
        dest.write(orig.read())

answered Aug 31, 2015 at 23:32

mingaleg

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3 Comments

Kevin Over a year ago

Use shutil.copyfileobj() or else you run out of RAM.

mingaleg Over a year ago

And don't forget to limit chunks size, or you run out of RAM whatever ;)

jeffpkamp Over a year ago

I think the problem comes before that point. it is calling my output a None object.

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