python/demos/demo_tapthebeat.py: play beats using pyaudio

diff --git a/python/demos/demo_tapthebeat.py b/python/demos/demo_tapthebeat.py
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+#! /usr/bin/env python
+
+""" A simple demo using aubio and pyaudio to play beats in real time
+
+Note you will need to have pyaudio installed: `pip install pyaudio`.
+
+Examples:
+    ./demo_tapthebeat.py ~/Music/track1.ogg
+
+When compiled with ffmpeg/libav, you should be able to open remote streams. For
+instance using youtube-dl (`pip install youtube-dl`):
+
+    ./demo_tapthebeat.py `youtube-dl -xg https://youtu.be/zZbM9n9j3_g`
+
+"""
+
+import sys
+import time
+import pyaudio
+import aubio
+import numpy as np
+
+win_s = 1024                # fft size
+hop_s = win_s // 2          # hop size
+
+# parse command line arguments
+if len(sys.argv) < 2:
+    print("Usage: %s <filename> [samplerate]" % sys.argv[0])
+    sys.exit(1)
+
+filename = sys.argv[1]
+
+samplerate = 0
+if len( sys.argv ) > 2: samplerate = int(sys.argv[2])
+
+# create aubio source
+a_source = aubio.source(filename, samplerate, hop_s)
+samplerate = a_source.samplerate
+
+# create aubio tempo detection
+a_tempo = aubio.tempo("default", win_s, hop_s, samplerate)
+
+# create a simple click sound
+click = 0.7 * np.sin(2. * np.pi * np.arange(hop_s) / hop_s * samplerate / 3000.)
+
+# pyaudio callback
+def pyaudio_callback(in_data, frame_count, time_info, status):
+    samples, read = a_source()
+    is_beat = a_tempo(samples)
+    if is_beat:
+        samples += click
+        #print ('tick') # avoid print in audio callback
+    audiobuf = samples.tobytes()
+    if read < hop_s:
+        return (audiobuf, pyaudio.paComplete)
+    return (audiobuf, pyaudio.paContinue)
+
+# create pyaudio stream with frames_per_buffer=hop_s and format=paFloat32
+p = pyaudio.PyAudio()
+pyaudio_format = pyaudio.paFloat32
+frames_per_buffer = hop_s
+n_channels = 1
+stream = p.open(format=pyaudio_format, channels=n_channels, rate=samplerate,
+        output=True, frames_per_buffer=frames_per_buffer,
+        stream_callback=pyaudio_callback)
+
+# start pyaudio stream
+stream.start_stream()
+
+# wait for stream to finish
+while stream.is_active():
+    time.sleep(0.1)
+
+# stop pyaudio stream
+stream.stop_stream()
+stream.close()
+# close pyaudio
+p.terminate()