js如何获取音视频的分贝

想获取到音视频声音的强度值，得到一份由强度值组成的数据，根据这份数据画对应的波形震动图

使用AudioContext API实现获取音频分贝值，并且将获取的数据画出对应的波形振动图的示例代码：

<html>
<head>
<script>
    window.AudioContext = window.AudioContext || window.webkitAudioContext;
    var audioCtx = new AudioContext();
    // 加载音频
    var audio = document.querySelector('audio');
    var audioSrc = audioCtx.createMediaElementSource(audio);
    var analyser = audioCtx.createAnalyser();
    // 将音频源连接到分析器
    audioSrc.connect(analyser);
    // 将分析器连接到目标节点
    analyser.connect(audioCtx.destination);
    // 获取音频的分贝值
    var frequencyData = new Uint8Array(analyser.frequencyBinCount);
    analyser.getByteFrequencyData(frequencyData);
    // 画出波形振动图
    var canvas = document.querySelector('.visualizer');
    var canvasCtx = canvas.getContext("2d");
    var WIDTH = canvas.width;
    var HEIGHT = canvas.height;
    function draw() {
        requestAnimationFrame(draw);
        analyser.getByteFrequencyData(frequencyData);
        canvasCtx.clearRect(0, 0, WIDTH, HEIGHT);
        var barWidth = (WIDTH / analyser.frequencyBinCount) * 2.5;
        var barHeight;
        var x = 0;
        for(var i = 0; i < analyser.frequencyBinCount; i++) {
            barHeight = frequencyData[i];
            canvasCtx.fillStyle = 'rgb(' + (barHeight+100) + ',50,50)';
            canvasCtx.fillRect(x,HEIGHT-barHeight/2,barWidth,barHeight/2);
            x += barWidth + 1;
        }
    };
    draw();
</script>
</head>
<body>
    <audio controls>
        <source src="audio.mp3" type="audio/mpeg">
    </audio>
    <canvas class="visualizer" width="300" height="200"></canvas>
</body>
</html>