How to pipe pygame camera data to ffmpeg in python?

Question

I'm trying to pipe pygame camera output to FFmpeg in ubuntu. But it is showing

Broken pipe error.

Here is my code:

proc = Popen(['ffmpeg', '-y', '-f', 'rawvideo', '-vcodec', 'rawvideo', '-r', '24', '-i', '-', '-vcodec', 'mpeg4', '-q:a', '5', '-r', '24', 'video.avi'], stdin=PIPE)

proc.stdin.write(pil_string_image)
for i in range(100):
  image = cam.get_image()
  pil_string_image = pg.image.tostring(image, "RGBA", False)
  proc.stdin.write(pil_string_image)
proc.stdin.close()
proc.stderr.close()
proc.wait()

I'm new to programming and like to learn programming by developing applications.