title: Trying to convert an mp3 file to a Numpy Array, and ffmpeg just hangs
body: <p>I'm working on a music classification methodology with Scikit-learn, and the first step in that process is converting a music file to a numpy array. </p>
  
  <p>After unsuccessfully trying to call ffmpeg from a python script, I decided to simply pipe the file in directly:</p>
  
  <pre><code>FFMPEG_BIN = "ffmpeg"
  cwd = (os.getcwd())
  dcwd = (cwd + "/temp")
  if not os.path.exists(dcwd): os.makedirs(dcwd)
  
  folder_path = sys.argv[1]
  f = open("test.txt","a")
  
  for f in glob.glob(os.path.join(folder_path, "*.mp3")):
      ff = f.replace("./", "/")
      print("Name: " + ff)
      aa = (cwd + ff)
  
      command = [ FFMPEG_BIN,
          '-i',  aa,
          '-f', 's16le',
          '-acodec', 'pcm_s16le',
          '-ar', '22000', # ouput will have 44100 Hz
          '-ac', '1', # stereo (set to '1' for mono)
          '-']
  
      pipe = sp.Popen(command, stdout=sp.PIPE, bufsize=10**8)
      raw_audio = pipe.proc.stdout.read(88200*4)
      audio_array = numpy.fromstring(raw_audio, dtype="int16")
      print (str(audio_array))
      f.write(audio_array + "\n")
  </code></pre>
  
  <p>The problem is, when I run the file, it starts ffmpeg and then does nothing:</p>
  
  <pre><code>[mp3 @ 0x1446540] Estimating duration from bitrate, this may be inaccurate
  Input #0, mp3, from '/home/don/Code/Projects/MC/Music/Spaz.mp3':
    Metadata:
      title           : Spaz
      album           : Seeing souns
      artist          : N*E*R*D
      genre           : Hip-Hop
      encoder         : Audiograbber 1.83.01, LAME dll 3.96, 320 Kbit/s, Joint Stereo, Normal quality
      track           : 5/12
      date            : 2008
    Duration: 00:03:50.58, start: 0.000000, bitrate: 320 kb/s
      Stream #0:0: Audio: mp3, 44100 Hz, stereo, s16p, 320 kb/s
  Output #0, s16le, to 'pipe:':
    Metadata:
      title           : Spaz
      album           : Seeing souns
      artist          : N*E*R*D
      genre           : Hip-Hop
      date            : 2008
      track           : 5/12
      encoder         : Lavf56.4.101
      Stream #0:0: Audio: pcm_s16le, 22000 Hz, mono, s16, 352 kb/s
      Metadata:
        encoder         : Lavc56.1.100 pcm_s16le
  Stream mapping:
    Stream #0:0 -&gt; #0:0 (mp3 (native) -&gt; pcm_s16le (native))
  Press [q] to stop, [?] for help
  </code></pre>
  
  <p>It just sits there, hanging, for far longer than the song is. What am I doing wrong here?,</p>