PCM Wave time stretch Write the smallest program performs a time stretch operation on a PCM Wave (.wav) file.

Rules:


Parameter input will by via whatever standard argument mechanism your language comes with, e.g. argv in C/C++, $_GET in PHP. Hard coded paths are not allowed.
First parameter will be a decimal value that represents the stretch coefficient. 1 means don't stretch, 2 means twice the length, 0.5 means half the length, 0.333 means one third the length. An example might be stretch.exe 1.5 c:\sound.wav
The time stretch operation does not need to perform pitch correction.
You must not drop samples to fit a compression (i.e. stretch &lt; 1). You should use interpolation, weighted mean, or a similar method.
Assume a WAVE PCM file with a RIFF header.
Assume 16-bits per sample (bonus if your code works for 8-bit and 24-bit audio)
You must handle any number of audio channels.
You must at least handle 11025, 22050 and 44100Hz sample rates, though the ability to handle arbitrary rates would be a bonus! :)
Your output file must keep the same sample rate, sample size and channel count as the input file.
The output file must be named "stretch.wav"
You may not use any 3rd party libraries or built-in functions for audio processing. The parsing of the WAV file and the time stretch operation must be your own code.


On Windows, the C:\Windows\Media directory contains plenty of WAV files to test with.
Ruby, 220 characters
s,n=$*
w=IO.binread(n).unpack r='s&lt;*'
x=[];t=[g=0]*c=w[11]
w[u=22..-1].each_slice(c){|f|g+=v=1.0/s.to_f
c.times{|h|t[h]+=f[h]*v}
(c.times{|h|x&lt;&lt;=m=t[h]/g;t[h]-=m};g-=1)until 1&gt;g}
w[u]=x;IO.binwrite'stretch.wav',w.pack(r)

This version works with ruby 1.9.3 with basic 16 bit files (e.g. no additional chunks) for any sample rate or number of channels.