//Get audio element.
var audio = document.getElementById("background_audio");

//Get current time/date.
var date = new Date();
date.setTime(+ date + (1 * 24 * 60 * 60 * 1000)); // _days_ * hours/day * mins/hour * sec/min * ms/s (Change first number to change how many days cookie is valid for)

//Check if mute cookie exists.
if (document.cookie.indexOf("mute=") == -1) {
    //It does not, lets create it!
    document.cookie = "mute=" + false + ";expires=" + date.toGMTString() + "; path=/";
    //Start playing audio!
    audio.play();
} else {
    //Check if mute cookie is set to false.
    if (getCookie("mute") == "false") {
        //It is, lets play!
        audio.play();
    }
}

function getCookie(name) {
    // getCookie function by Chirp Internet: www.chirp.com.au
    var re = new RegExp(name + "=([^;]+)");
    var value = re.exec(document.cookie);
    return value != null ? unescape(value[1]) : null;
}

//On play/mute button/link click.
document.getElementById("mute").addEventListener("click",function(e) {
    e = e || window.event;
    if (getCookie("mute") == "false") {
        //If mute cookie is set to false, mute audio.
        audio.muted = true;
    } else {
        //If mute cookie is set to true, unmute audio.
        audio.muted = false;
        //Check if audio has been started before.
        if (audio.paused || audio.currentTime > 0) {
            //It has not, lets play it!
            audio.play();
        }
    }
    //Set/update mute cookie with new audio muted value.
    document.cookie = "mute=" + audio.muted + ";expires=" + date.toGMTString() + "; path=/";
    e.preventDefault();
}, false);