python/demos/demo_wav2midi.py: add simple midi file writer using mido (closes: #134)

diff --git a/python/demos/demo_wav2midi.py b/python/demos/demo_wav2midi.py
new file mode 100755 (executable)
index 0000000..f503dc0
--- /dev/null
+++ b/python/demos/demo_wav2midi.py
@@ -0,0 +1,81 @@
+#! /usr/bin/env python
+
+# Simple demo to extract notes from a sound file, and store them in a midi file
+# using mido.
+#
+# Install mido: `pip instal mido`
+#
+# Documentation: https://mido.readthedocs.io/
+
+import sys
+from aubio import source, notes
+from mido import Message, MetaMessage, MidiFile, MidiTrack, second2tick, bpm2tempo
+
+if len(sys.argv) < 3:
+    print("Usage: %s <filename> <output> [samplerate]" % sys.argv[0])
+    sys.exit(1)
+
+filename = sys.argv[1]
+midioutput = sys.argv[2]
+
+downsample = 1
+samplerate = 44100 // downsample
+if len( sys.argv ) > 3: samplerate = int(sys.argv[3])
+
+win_s = 512 // downsample # fft size
+hop_s = 256 // downsample # hop size
+
+s = source(filename, samplerate, hop_s)
+samplerate = s.samplerate
+
+tolerance = 0.8
+
+notes_o = notes("default", win_s, hop_s, samplerate)
+
+print("%8s" % "time","[ start","vel","last ]")
+
+# create a midi file
+mid = MidiFile()
+track = MidiTrack()
+mid.tracks.append(track)
+
+ticks_per_beat = mid.ticks_per_beat # default: 480
+bpm = 120 # default midi tempo
+
+tempo = bpm2tempo(bpm)
+track.append(MetaMessage('set_tempo', tempo=tempo))
+track.append(MetaMessage('time_signature', numerator=4, denominator=4))
+
+def frames2tick(frames, samplerate=samplerate):
+    sec = frames / float(samplerate)
+    tick = int(second2tick(sec, ticks_per_beat, tempo))
+    return tick
+
+sec = 7
+previous_note = None
+
+last_time = 0
+
+# total number of frames read
+total_frames = 0
+while True:
+    samples, read = s()
+    new_note = notes_o(samples)
+    if (new_note[0] != 0):
+        note_str = ' '.join(["%.2f" % i for i in new_note])
+        print("%.6f" % (total_frames/float(samplerate)), new_note)
+        delta = frames2tick(total_frames) - last_time
+        if new_note[2] > 0:
+            track.append(Message('note_off', note=int(new_note[2]),
+                velocity=127, time=0)
+                )
+        track.append(Message('note_on',
+            note=int(new_note[0]),
+            velocity=int(new_note[1]),
+            time=delta)
+            )
+        last_time = frames2tick(total_frames)
+    total_frames += read
+    if read < hop_s: break
+
+mid.save(midioutput)