NPR mp3 url decoder

gistfile1.js

NPR = {};
NPR.base64 = {};

// Code below belongs to NPR
NPR.base64.PADCHAR = '=';

NPR.base64.ALPHA = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
NPR.base64.makeDOMException = function () {
    var e, tmp;
    try {
        return new DOMException(DOMException.INVALID_CHARACTER_ERR);
    } catch (tmp) {
        var ex = new Error("DOM Exception 5");
        ex.code = ex.number = 5;
        ex.name = ex.description = "INVALID_CHARACTER_ERR";
        ex.toString = function () {
            return 'Error: ' + ex.name + ': ' + ex.message;
        };
        return ex;
    }
}
NPR.base64.getbyte64 = function (s, i) {
    var idx = NPR.base64.ALPHA.indexOf(s.charAt(i));
    if (idx === -1) {
        throw NPR.base64.makeDOMException();
    }
    return idx;
}
NPR.base64.decode = function (s) {
    s = '' + s;
    var getbyte64 = NPR.base64.getbyte64;
    var pads, i, b10;
    var imax = s.length
    if (imax === 0) {
        return s;
    }
    if (imax % 4 !== 0) {
        throw NPR.base64.makeDOMException();
    }
    pads = 0
    if (s.charAt(imax - 1) === NPR.base64.PADCHAR) {
        pads = 1;
        if (s.charAt(imax - 2) === NPR.base64.PADCHAR) {
            pads = 2;
        }
        imax -= 4;
    }
    var x = [];
    for (i = 0; i < imax; i += 4) {
        b10 = (getbyte64(s, i) << 18) | (getbyte64(s, i + 1) << 12) | (getbyte64(s, i + 2) << 6) | getbyte64(s, i + 3);
        x.push(String.fromCharCode(b10 >> 16, (b10 >> 8) & 0xff, b10 & 0xff));
    }
    switch (pads) {
    case 1:
        b10 = (getbyte64(s, i) << 18) | (getbyte64(s, i + 1) << 12) | (getbyte64(s, i + 2) << 6);
        x.push(String.fromCharCode(b10 >> 16, (b10 >> 8) & 0xff));
        break;
    case 2:
        b10 = (getbyte64(s, i) << 18) | (getbyte64(s, i + 1) << 12);
        x.push(String.fromCharCode(b10 >> 16));
        break;
    }
    return x.join('');
}
NPR.base64.getbyte = function (s, i) {
    var x = s.charCodeAt(i);
    if (x > 255) {
        throw NPR.base64.makeDOMException();
    }
    return x;
}
NPR.base64.encode = function (s) {
    if (arguments.length !== 1) {
        throw new SyntaxError("Not enough arguments");
    }
    var padchar = NPR.base64.PADCHAR;
    var alpha = NPR.base64.ALPHA;
    var getbyte = NPR.base64.getbyte;
    var i, b10;
    var x = [];
    s = '' + s;
    var imax = s.length - s.length % 3;
    if (s.length === 0) {
        return s;
    }
    for (i = 0; i < imax; i += 3) {
        b10 = (getbyte(s, i) << 16) | (getbyte(s, i + 1) << 8) | getbyte(s, i + 2);
        x.push(alpha.charAt(b10 >> 18));
        x.push(alpha.charAt((b10 >> 12) & 0x3F));
        x.push(alpha.charAt((b10 >> 6) & 0x3f));
        x.push(alpha.charAt(b10 & 0x3f));
    }
    switch (s.length - imax) {
    case 1:
        b10 = getbyte(s, i) << 16;
        x.push(alpha.charAt(b10 >> 18) + alpha.charAt((b10 >> 12) & 0x3F) + padchar + padchar);
        break;
    case 2:
        b10 = (getbyte(s, i) << 16) | (getbyte(s, i + 1) << 8);
        x.push(alpha.charAt(b10 >> 18) + alpha.charAt((b10 >> 12) & 0x3F) + alpha.charAt((b10 >> 6) & 0x3f) + padchar);
        break;
    }
    return x.join('');
}

NPR.unpack = function (s) {
    return NPR.base64.decode(NPR.rot13(s));
}
NPR.rot13 = function (str) {
    return (str + '').replace(/[a-z]/gi,

    function (s) {
        return String.fromCharCode(s.charCodeAt(0) + (s.toLowerCase() < 'n' ? 13 : -13));
    });
}