Python Pyaudio录制x秒，同时输入通过树形文件夹

我有一个Python函数，当它检测到噪音时，当声音比树桩大时，就开始录制，但我需要它只录制一段特定的时间（例如两秒），但我不知道如何做。我试过利用时间睡觉，但没用。我怎么做？这是我的职责：

def stt(language, threshold=THRESHOLD, num_phrases=-1):
    """
    Listens to Microphone, extracts phrases from it and sends it to 
    Google's TTS service and returns response. a "phrase" is sound 
    surrounded by silence (according to threshold). num_phrases controls
    how many phrases to process before finishing the listening process 
    (-1 for infinite). 
    """

    #Open stream
    p = pyaudio.PyAudio()

    stream = p.open(format=FORMAT,
                    channels=CHANNELS,
                    rate=RATE,
                    input=True,
                    frames_per_buffer=CHUNK)

    print "* Listening mic. "
    audio2send = []
    cur_data = ''  # current chunk  of audio data
    rel = RATE/CHUNK
    slid_win = deque(maxlen=SILENCE_LIMIT * rel)
    #Prepend audio from 0.5 seconds before noise was detected
    prev_audio = deque(maxlen=PREV_AUDIO * rel) 
    started = False
    n = num_phrases
    response = []

    while (num_phrases == -1 or n > 0):
        cur_data = stream.read(CHUNK)
        slid_win.append(math.sqrt(abs(audioop.avg(cur_data, 4))))
        #print slid_win[-1]
        if(sum([x > THRESHOLD for x in slid_win]) > 0):
            if(not started):
                print "Starting record of phrase"
                started = True
            audio2send.append(cur_data)
        elif (started is True):
            print "Finished"
            # The limit was reached, finish capture and deliver.
            filename = save_speech(list(prev_audio) + audio2send, p)
            # Send file to Google and get response
            r = stt_google_wav(filename, language) 
            if num_phrases == -1:
                print r
            else:
                response.append(r)
            # Remove temp file. Comment line to review.
            os.remove(filename)
            # Reset all
            started = False
            slid_win = deque(maxlen=SILENCE_LIMIT * rel)
            prev_audio = deque(maxlen=0.5 * rel) 
            audio2send = []
            n -= 1
            print "Listening ..."
        else:
            prev_audio.append(cur_data)

    print "* Done recording"
    stream.close()
    p.terminate()

    return response

非常感谢