python/demos/demo_timestretch.py: add timescale algorithm

diff --git a/python/demos/demo_timestretch.py b/python/demos/demo_timestretch.py
new file mode 100755 (executable)
index 0000000..8569a44
--- /dev/null
+++ b/python/demos/demo_timestretch.py
@@ -0,0 +1,110 @@
+#! /usr/bin/env python
+
+# Implementation of the timescale algorithm according to Dan Ellis, *A Phase
+# Vocoder in Matlab*.  http://www.ee.columbia.edu/~dpwe/resources/matlab/pvoc/
+
+# This file follows the original implementation, with analysis in a first pass,
+# and synthesis in a second pass.
+
+import sys
+from aubio import source, sink, pvoc, mfcc, cvec
+from aubio import unwrap2pi, float_type
+import numpy as np
+
+win_s = 1024
+hop_s = win_s / 8 # 87.5 % overlap
+
+warmup = win_s // hop_s - 1
+
+if len(sys.argv) < 3:
+    print("Usage: %s <source_filename> <output_filename> <rate> [samplerate]".format(sys.argv[0]))
+    print("""Examples:
+    # twice faster
+    {0} track_01.mp3 track_01_faster.wav 2.0
+    # twice slower
+    {0} track_02.flac track_02_slower.wav 0.5
+    # one and a half time faster, resampling first the input to 22050
+    {0} track_02.flac track_02_slower.wav 1.5 22050""".format(sys.argv[0]))
+    sys.exit(1)
+
+source_filename = sys.argv[1]
+output_filename = sys.argv[2]
+rate = float(sys.argv[3])
+
+samplerate = 0 if len(sys.argv) < 5 else int(sys.argv[4])
+source_in = source(source_filename, samplerate, hop_s)
+samplerate = source_in.samplerate
+p = pvoc(win_s, hop_s)
+
+# allocate memory to store norms and phases
+n_blocks = source_in.duration // hop_s + 1
+# adding an empty frame at end of spectrogram
+norms  = np.zeros((n_blocks + 1, win_s // 2 + 1), dtype = float_type)
+phases = np.zeros((n_blocks + 1, win_s // 2 + 1), dtype = float_type)
+
+block_read = 0
+while True:
+    # read from source
+    samples, read = source_in()
+    # compute fftgrain
+    spec = p(samples)
+    # store current grain
+    norms[block_read] = spec.norm
+    phases[block_read] = spec.phas
+    # until end of file
+    if read < hop_s: break
+    # increment block counter
+    block_read += 1
+
+# just to make sure
+#source_in.close()
+
+sink_out = sink(output_filename, samplerate)
+
+# interpolated time steps (j = alpha * i)
+steps = np.arange(0, n_blocks, rate, dtype = float_type)
+# initial phase
+phas_acc = phases[0]
+# excepted phase advance in each bin
+phi_advance = np.linspace(0, np.pi * hop_s, win_s / 2 + 1).astype (float_type)
+
+new_grain = cvec(win_s)
+
+for (t, step) in enumerate(steps):
+
+    frac = 1. - np.mod(step, 1.0)
+    # get pair of frames
+    t_norms = norms[int(step):int(step+2)]
+    t_phases = phases[int(step):int(step+2)]
+
+    # compute interpolated frame
+    new_grain.norm = frac * t_norms[0] + (1. - frac) * t_norms[1]
+    new_grain.phas = phas_acc
+    #print t, step, new_grain.norm
+    #print t, step, phas_acc
+
+    # psola
+    samples = p.rdo(new_grain)
+    if t > warmup: # skip the first few frames to warm up phase vocoder
+        # write to sink
+        sink_out(samples, hop_s)
+
+    # calculate phase advance
+    dphas = t_phases[1] - t_phases[0] - phi_advance
+    # unwrap angle to [-pi; pi]
+    dphas = unwrap2pi(dphas)
+    # cumulate phase, to be used for next frame
+    phas_acc += phi_advance + dphas
+
+for t in range(warmup + 1): # purge the last frames from the phase vocoder
+    new_grain.norm[:] = 0
+    new_grain.phas[:] = 0
+    samples = p.rdo(new_grain)
+    sink_out(samples, read if t == warmup else hop_s)
+
+# just to make sure
+#sink_out.close()
+
+format_out = "read {:d} blocks from {:s} at {:d}Hz and rate {:f}, wrote {:d} blocks to {:s}"
+print (format_out.format(block_read, source_filename, samplerate, rate,
+    len(steps), output_filename))