python mp3/ogg stream encoding

import fcntl, os, signal
from select import select
from subprocess import Popen, PIPE
from threading import Thread
import time

def unblock_fd(fd):
    fl = fcntl.fcntl(fd, fcntl.F_GETFL)
    fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)

class Converter(object):
    SIZE = 1024

    def __init__(self, cmd):
        self.process = Popen(cmd, shell=True, stdin=PIPE, stdout=PIPE)
        unblock_fd(self.process.stdout)

    def start(self, chunk_processed):
        while self.process.poll() is None:
            r, _, _ = select([self.process.stdout], [], [])
            if r:
                data = r[0].read(self.SIZE)
                if data:
                    chunk_processed(data)

    def feed(self, data):
        self.process.stdin.write(data)
        self.process.stdin.flush()

    def stop(self):
        self.process.stdin.close()
        self.process.send_signal(signal.SIGPIPE)
        self.process.wait()

def writer(converter):
    for _ in xrange(10):
        converter.feed('String\n')
        time.sleep(0.1)

    converter.stop()

def reader(data):
    print data,

converter = Converter('grep --line-buffered -o Str')
t = Thread(target=writer, args=(converter,))
t.daemon = True
t.start()

converter.start(reader)