ffmpeg python

import  numpy as np
from subprocess import Popen,PIPE
import sys
p = Popen('ffmpeg -y -f rawvideo -pix_fmt gray -s:v 1280x720 -r 25 -i - 1.mp4'.split(" "),
          stdin=PIPE,
          stderr=sys.stdout,
          stdout=sys.stdout
          )
a = np.zeros((1280,720),np.uint8)
for cnt in range(10000):
    for x in range(1280):
        for y in range(720):
            if ((cnt + x%8)  %2)!=((y%8)%2):
                    a[x,y] = 255
    #a.tofile(sys.stdout)
    #print(p.communicate(a.tobytes()))
    p.stdin.write(a.tobytes())
p.stdin.close()