The first two lines of the encoder.html file are this:
<html>
<script type="text/javascript" src="php.default.min.js"></script>
That aside, it doesn't run in Chrome (haven't tried other browsers, sorry), and I see little that describes it or the method, and haven't sat down and worked through the logic. The effectiveness of steganography depends heavily on how you hide the data though, and I don't see anything that implies I should trust this setup over something else.
Also, I have doubts that this works 100% in floating point math:
var t = 2091639 * s0 + c * 2.3283064365386963e-10; // 2^-32
s0 = s1;
s1 = s2;
return s2 = t - (c = t | 0);