Mp3 Music Player with Album Art, that plays songs and playlist on click with previous and Next song selection

I am creating a basic webplayer for my website. right now I have it set to a simple source file "src=mp3song.mp3

I am trying to get it to where I can use javascript to auto play a select song and load a song or playlist on click. as well as select next or previous song in the playlist. meaning I will have a music library included on my website. it will consist of a thumbnail that will open in a lightbox. in the lightbox it will show The artwork for the title and the song list. each song will have its own audio play button and there will be an button to play the entire albums playlist.

<script>
    var player;
    var intv;
    var slider;
    //Init
    //
    ////////////////////////////
    window.onload = function()
    {
        document.getElementById('btnPlay').addEventListener('click', playMusic, false);
        document.getElementById('btnPause').addEventListener('click', pauseMusic, false);
        document.getElementById('btnStop').addEventListener('click', stopMusic, false);
        document.getElementById('btnVolUp').addEventListener('click', volUp, false);
        document.getElementById('btnVolDown').addEventListener('click', volDown, false);
        player = document.getElementById('player');
        slider = document.getElementById('sliderTime');
        slider.addEventListener('change', reposition, false);
    }

    function reposition()
    {
        player.currentTime = slider.value;
    }


    //Volume Controls
    //
    // 0.0  Silent - 1.0 Full Volume
    /////////////////////////////
    function volUp()
    {
        if(player.volume < 1)
        {
            player.volume += 0.1;
            console.log(player.volume);
        } else
        {
            player.volume = 1;
        }
    }

    function volDown()
    {
        if(player.volume > 0)
        {
            player.volume -= 0.1;
            console.log(player.volume);
        } else
        {
            player.volume = 0;
        }
    }
    //Music Play Controls
    //
    ///////////////////////////
    function playMusic()
    {
        player.play();
        intv = setInterval(update, 100);
        slider.max = player.duration;
    }

    function update()
    {
        document.getElementById('songTime').innerHTML = millisToMins(player.currentTime);
        slider.value = player.currentTime;
    }

    function millisToMins(seconds)
    {
        var numminutes = Math.floor((((seconds % 31536000) % 86400) % 3600) / 60);
        var numseconds = (((seconds % 31536000) % 86400) % 3600) % 60;
        if (numseconds >= 10)
        {
            return "Time Elapsed: " + numminutes + ":" + Math.round(numseconds);
        } else
        {
            return "Time Elapsed: " + numminutes + ":0" + Math.round(numseconds);
        }
    }

    function pauseMusic()
    {
        player.pause();
        clearInterval(intv);
    }

    function stopMusic()
    {
        player.pause();
        player.currentTime = 0;
        clearInterval(intv);
    }
</script>
</head>