Detailed explanation of HTML5 music visualization code

musicVisualizer.ac = new(window.AudioContext || window.webkitAudioContext)(); //实例化一个音频类型window.AudioContext,后面是为了兼容Chrome浏览器 function musicVisualizer(obj) { this.source = null; //初始化音频资源变量 this.analyser = musicVisualizer.ac.createAnalyser(); //这一步是非常重要的，createAnalyser()可以创建一个／AnalyserNode／用来获取音频的各项数据，实现音乐可视化 this.size = obj.size; //这里是 index.js里面实例化原型的参数obj中的大小属性 this.analyser.fftSize = this.size * 2; //fftsize(AnalyserNode的一个属性)是一个无符号长整型的值, 用于确定频域的 FFT (快速傅里叶变换) 的大小.fftSize 属性的值必须是从32到32768范围内的2的非零幂; 其默认值为2048.总之最后获取到的数组长度应该是fftSize值的一半，还应该保证它是以2为底的幂。 this.xhr = new XMLHttpRequest();//这个就很熟悉了对于大家而言，创建ajax对象 this.analyser.connect(musicVisualizer.ac.destination); //musicVisualizer.ac.destination是音频要最终输出的目标，所有节点中的最后一个节点应该再连接到musicVisualizer.ac.destination播放声音 this.visualizer = obj.visualizer; //这里是 index.js里面实例化原型的参数obj中的canvas绘画音乐节点实现节奏可视化 this.visualize(); } musicVisualizer.prototype.load = function(url, fun) { this.xhr.abort();//停止正在进行的ajax请求 this.xhr.open("GET", url); this.xhr.responseType = "arraybuffer"; var self = this; this.xhr.onload = function() { fun(self.xhr.response); }; this.xhr.send(); }; musicVisualizer.prototype.decode = function(arraybuffer, fun) { musicVisualizer.ac.decodeAudioData(arraybuffer, function(buffer) { //decodeAudioData用于异步解码音频文件中的arrayBuffer数据 fun(buffer); }, function(err) { console.log(err); }); }; musicVisualizer.prototype.stop = function() { this.source[this.source.stop ? "stop" : "noteOff"](0); }; musicVisualizer.prototype.visualize = function() { var arr = new Uint8Array(this.analyser.frequencyBinCount); //frequencyBinCount通常是可视化数据值的数量，为fftSize的一半 requestAnimationFrame = window.requestAnimationFrame || webkitRequestAnimationFrame || mozRequestAnimationFrame; //window.requestAnimationFrame() 方法告诉浏览器您希望执行动画，并请求浏览器调用指定的函数在下一次重绘之前更新动画。该方法将在重绘之前调用的回调作为参数。 var self = this; function v() { self.analyser.getByteFrequencyData(arr); //getByteFrequmencyData把当前频率数据复制到传入其中的Uint8Array self.visualizer(arr); requestAnimationFrame(v); } requestAnimationFrame(v); }; musicVisualizer.prototype.play = function(url) { var self = this; this.source && this.stop(); this.load(url, function(arraybuffer) { self.decode(arraybuffer, function(buffer) { var bs = musicVisualizer.ac.createBufferSource(); //createBufferSource() 方法用于创建一个新的AudioBufferSourceNode接口, 该接口可以通过AudioBuffer 对象来播放音频数据. AudioBuffer对象可以通过AudioContext.createBuffer 来创建或者通过 AudioContext.decodeAudioData成功解码音轨后获取. bs.connect(self.analyser); bs.buffer = buffer; bs[bs.start ? "start" : "noteOn"](0); self.source = bs; }); }); };

var size = 64; var box = $("#box")[0]; var height, width; var canvas = document.createElement('canvas'); var ctx = canvas.getContext("2d"); box.appendChild(canvas); var Dots = []; draw.type = "column"; window.onresize = resize; var line; var mv = new musicVisualizer({ size: size, visualizer: draw }); var clickMusic = (function () { var lis = $(".music li"); lis.click(function() { var i = $(this).index(); lis.css('color', 'white'); lis.eq(i).css('color', 'grey'); mv.play('./musics/' + lis.eq(i).html()); }); })(); function random(m, n) { return Math.round(Math.random() * (n - m) + m); } function getDots() { Dots = []; for (var i = 0; i < size; i++) { var x = random(0, width); var y = random(0, height); var color = "rgba(" + random(0, 255) + "," + random(0, 255) + "," + random(0, 255) + ",0)"; Dots.push({ x: x, y: y, color: color, cap: 0, dx: random(1, 4) }); }; } var resize = (function () { height = box.clientHeight; width = box.clientWidth; canvas.height = height; canvas.width = width; line = ctx.createLinearGradient(0, 0, 0, height); line.addColorStop(0, "pink"); line.addColorStop(0.5, "grey"); line.addColorStop(1, "lightblue"); getDots(); })(); function draw(arr) { ctx.clearRect(0, 0, width, height); var w = width / size; var cw = w * 0.6; var ch = cw; ctx.fillStyle = line; for (var i = 0; i < size; i++) { var o = Dots[i]; if (draw.type == "column") { var h = arr[i] / 256 * height; ctx.fillRect(w * i, height - h, cw, h); ctx.fillRect(w * i, height - (o.cap + ch), cw, ch); o.cap--; if (o.cap < 0) { o.cap = 0; } if (h > 0 && o.cap < h + 30) { o.cap = h + 30 > height - ch ? height - ch : h + 30; } } else if (draw.type == "dot") { ctx.beginPath(); var r = 10 + arr[i] / 256 * (height > width ? width : height) / 10; ctx.arc(o.x, o.y, r, 0, Math.PI * 2, true); var circle = ctx.createRadialGradient(o.x, o.y, 0, o.x, o.y, r); circle.addColorStop(0, "white"); circle.addColorStop(1, o.color); ctx.fillStyle = circle; ctx.fill(); o.x += o.dx; o.x = o.x > width ? 0 : o.x; } } } var changeStyle = (function () { var spans = $(".musicList span"); spans.click(function() { var i = $(this).index(); spans.removeClass('selected') .eq(i).addClass('selected'); draw.type = spans.eq(i).attr('type'); }); })();