import subprocess
import sys
from Tkinter import Tk, Button, mainloop
from threading import Thread

master = Tk()

film = '/Volumes/speicher/Rise Of The Footsoldier/Rise of the Footsoldier - CD1.avi'

def start(film=film):
    global popen
    popen = subprocess.Popen(['mplayer', film],
                             stdin=subprocess.PIPE,
                             stdout=subprocess.PIPE)

def pause():
    popen.communicate('p')


start_button = Button(master, text=u'Film starten', command=start)
pause_button = Button(master, text=u'Film pausieren',
                      command=lambda: Thread(target=pause).start())
start_button.pack()
pause_button.pack()

mainloop()