Web-Audio-Fades/scurve.html at master · naomiaro/Web-Audio-Fades · GitHub

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<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>S-Curve Fade Demo</title>
<style>
    .hidden {
        display: none;
    }
</style>
</head>
<body>

  <div id='play' class='hidden'>Play</div>
  <div id='stop'>Stop</div>

<script type="text/javascript">
(function(){

    //creating a curve to simulate an S-curve with setValueCurveAtTime.
    var createSCurveBuffer = function createSCurveBuffer(length, phase) {
        var curve = new Float32Array(length),
            i;

        for (i = 0; i < length; ++i) {
            //scale the curve to be between 0-1
            curve[i] = (Math.sin((Math.PI * i / length) - phase)) /2 + 0.5;
        }
        return curve;
    };

    /*
        Test script to demonstrate an exponential fade.
    */
    var ctx = new AudioContext(),
        url = 'Legend.mp3',
        audio = new Audio(url),
        gainNode = ctx.createGain(),
        source,
        start,
        end,
        play,
        stop;

        audio.addEventListener('canplaythrough', function(){
            source = ctx.createMediaElementSource(audio);
            source.connect(gainNode);
            gainNode.connect(ctx.destination);

            curve = createSCurveBuffer(ctx.samplerate, (Math.PI/2));

            start = ctx.currentTime;
            gainNode.gain.setValueCurveAtTime(curve, start, 5);

            audio.play();
        });

        play = document.getElementById("play");
        play.addEventListener('click', function(e){
            play.className='hidden';
            stop.className='';
            audio.play();
        })

        stop = document.getElementById("stop");
        stop.addEventListener('click', function(e){
            play.className='';
            stop.className='hidden';
            audio.pause();
        })

})();
</script>
</body>
</html>