demos/demo_onset_file.py: added onset example

diff --git a/python/demos/demo_onset_file.py b/python/demos/demo_onset_file.py
new file mode 100755 (executable)
index 0000000..cea9698
--- /dev/null
+++ b/python/demos/demo_onset_file.py
@@ -0,0 +1,53 @@
+#! /usr/bin/env python
+
+import sys
+from aubio import onset, source
+from numpy import array, hstack, zeros
+
+win_s = 512                 # fft size
+hop_s = win_s / 2           # hop size
+samplerate = 44100
+downsample = 2              # used to plot n samples / hop_s
+
+if len(sys.argv) < 2:
+    print "Usage: %s <filename>" % sys.argv[0]
+    sys.exit(1)
+
+filename = sys.argv[1]
+onsets = []
+oldonsets = []
+
+s = source(filename, samplerate, hop_s)
+o = onset("default", win_s, hop_s)
+
+block_read = 0
+allsamples_max = zeros(0,)
+while True:
+    samples, read = s()
+    new_maxes = (abs(samples.reshape(hop_s/downsample, downsample))).max(axis=0)
+    allsamples_max = hstack([allsamples_max, new_maxes])
+    isbeat = o(samples)
+    if isbeat:
+        thisbeat = (block_read - 4. + isbeat[0]) * hop_s / samplerate
+        print "%.4f" % thisbeat
+        onsets.append (thisbeat)
+        # old onset
+        thisbeat = (block_read - 3. ) * hop_s / samplerate
+        oldonsets.append (thisbeat)
+    block_read += 1
+    if read < hop_s: break
+
+# do plotting
+from numpy import arange
+from pylab import plot, show, xlabel, ylabel, legend, ylim, subplot, axis
+allsamples_max = (allsamples_max > 0) * allsamples_max
+allsamples_max_times = [ float(t) * hop_s / downsample / samplerate for t in range(len(allsamples_max)) ]
+plot(allsamples_max_times,  allsamples_max, '-b')
+plot(allsamples_max_times, -allsamples_max, '-b')
+axis(xmin = 0., xmax = max(allsamples_max_times) )
+for stamp in onsets: plot([stamp, stamp], [-1., 1.], '.-r')
+for stamp in oldonsets: plot([stamp, stamp], [-1., 1.], '.-g')
+xlabel('time (s)')
+ylabel('amplitude')
+show()
+