Best approach to decode Youtube cipher signature using PHP or JS

Question

Youtube is using cipher signature for some of the videos when the use_cipher_signature = true in the dictionary returned through http://www.youtube.com/get_vid

Answer 1

Ye old s.ytimg.com/yts/jsbin/html5player-vfltdb6U3.js is now 404 and the new URL i think looks a bit more like hxxps://s.ytimg.com/yts/jsbin/player-en_US-vfl_cdzrt/base.js

if you search the JavaScript you will find a bit of code that looks like this

function(a,b,c)
{
a=new Mr(a);
a.set("alr","yes");a.set("keepalive","yes");a.set("ratebypass","yes");a.set("mime",(0,window.encodeURIComponent)(b.mimeType.split(";")[0]));c&&a.set("signature",xr(c));return a},Jt=function(a,b){var c=Yr(b,"id"),c=c.replace(":",";");..............
}

The xr function that the above code calls looks like this

xr=function(a)
{
a=a.split("");
wr.rF(a,54);
wr.fs(a,75);
wr.N0(a,1);
wr.rF(a,52);
wr.N0(a,3);
wr.fs(a,31);
wr.rF(a,16);
wr.fs(a,38);
return a.join("")
}

After that i start to get a bit lost with the javascript and could do with a bit of help myself but talking about this on the code project gets you in troube.