js代码

<script type="text/javascript">

window.onload = function () {
 
 var file = document.getElementById("file");
 var audio = document.getElementById("audio");

 file.onchange = function () {
     //part1: 画布
     var canvas = document.getElementById("canvas");
     var context = canvas.getContext("2d");

     canvas.width = window.innerWidth;
     canvas.height = window.innerHeight;
     var WIDTH = canvas.width;
     var HEIGHT = canvas.height;

     //part2: 音频
     var files = this.files;//声音文件
     audio.src = URL.createObjectURL(files[0]);
     audio.load();

     //part3: 分析器
     var AudCtx = new AudioContext();//音频内容
     var src = AudCtx.createMediaElementSource(audio);
     var analyser = AudCtx.createAnalyser();

     src.connect(analyser);
     analyser.connect(AudCtx.destination);
     analyser.fftSize = 128;//快速傅里叶变换, 必须为2的N次方

     var bufferLength = analyser.frequencyBinCount;// = fftSize * 0.5

     //part4: 变量
     var barWidth = (WIDTH / bufferLength) - 1;//间隔1px
     var barHeight;

     var dataArray = new Uint8Array(bufferLength);//8位无符号定长数组

     //part5: 动态监听
     function renderFrame() {
         requestAnimationFrame(renderFrame);//方法renderFrame托管到定时器，无限循环调度，频率<16.6ms/次

         context.fillStyle = "#000";//黑色背景
         context.fillRect(0, 0, WIDTH, HEIGHT);//画布拓展全屏,动态调整

         analyser.getByteFrequencyData(dataArray);//获取当前时刻的音频数据

         //part6: 绘画声压条
         var x = 0;
         for (var i = 0; i < bufferLength; i++) {
             var data = dataArray[i];//int,0~255

             var percentV = data / 255;//纵向比例
             var percentH = i / bufferLength;//横向比例

             barHeight = HEIGHT * percentV;

             //gbk,0~255
             var r = 255 * percentV;//值越大越红
             var g = 255 * percentH;//越靠右越绿
             var b = 50;

             context.fillStyle = "rgb(" + r + "," + g + "," + b + ")";
             context.fillRect(x, HEIGHT - barHeight, barWidth, barHeight);

             x += barWidth + 1;//间隔1px
         }
     }

     renderFrame();

     //part7: 播放声音
     audio.play();
 };
};
</script>