function encodeBase64(d) {
        if (!d) return null;
        var charMap = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
               + "abcdefghijklmnopqrstuvwxyz"
               + "0123456789+/=";
        var out="";
        for (var count=0,i=0; i<d.length; ) {
            var chr1,chr2,chr3,enc1,enc2,enc3,enc4="";
            chr1=d[i++]; chr2=d[i++]; chr3=d[i++];
            enc1=chr1 >> 2;
            enc2=((chr1 & 0x03) << 4) | (chr2 >> 4);
            enc3=((chr2 & 0x0F) << 2) | (chr3 >> 6);
            enc4=chr3 & 0x3F;
            if (isNaN(chr2)) enc3=enc4=64;
            else if (isNaN(chr3)) enc4=64;
            out+=charMap.charAt(enc1)
               + charMap.charAt(enc2)
               + charMap.charAt(enc3)
               + charMap.charAt(enc4);
        }
        return out;
    };
    var base64=encodeBase64(new Uint8Array(data));