[前端]利用WebAudioAPI获取音频频谱（html5音频可

项目希望可以把音频可视化，有条随声音波动的曲线或者是像唱吧那种。开始是搜到了腾讯大腿（TGideas）写的audio可视化组件，想着直接用，后来各种原因还是打算自己重新写一个……虽然明显写得low了很多。
腾讯大腿的audio组件地址
http://www.3fwork.com/b403/001620MYM013253/
GitHub
https://github.com/tgideas/motion/blob/master/component/src/main/audio/audio.js

然后参照了官方api
https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API
还有一篇也是audio可视化的文章
http://www.mizuiren.com/330.html

注意audioContext.currentTime是从audioContext开始创建之后开始计算的

代码：

var Visualizer = function(config) {
    this.audioContext = null;
    this.analyser = null;
    this.source = null; //the audio source
    this.config = config;
    this.frequency = [];
    this.playing = false;
    this.ready = false;
    this.loadFailed = false;
};
Visualizer.prototype = {
    init: function () {
        this._prepare();
        this.getData();
        this._analyser();
    },
    _prepare: function () {
        //实例化一个音频上下文类型window.AudioContext。目前Chrome和Firefox对其提供了支持，但需要相应前缀，Chrome中为window.webkitAudioContext，Firefox中为mozAudioContext。
        // 所以为了让代码更通用，能够同时工作在两种浏览器中，只需要一句代码将前缀进行统一即可。
        window.AudioContext = window.AudioContext || window.webkitAudioContext || window.mozAudioContext || window.msAudioContext;
        try {
            this.audioContext = new AudioContext();
 
        } catch (e) {
            console.log(e);
        }
    },
    _analyser: function () {
        var that = this;
        that.analyser = that.audioContext.createAnalyser();
        that.analyser.smoothingTimeConstant = 0.85;
        that.analyser.fftSize = 32;//傅里叶变换参数 简化成16个元素数组
        //将source与分析器连接
        that.source.connect(that.analyser);
        //将分析器与destination连接，这样才能形成到达扬声器的通路
        that.analyser.connect(that.audioContext.destination);
        that.frequency = new Uint8Array(that.analyser.frequencyBinCount);

    },
    getData: function () {
        var that = this;
        //建立缓存源
        that.source = that.audioContext.createBufferSource();
        var request = new XMLHttpRequest();
        //请求资源
        request.open('GET', that.config.url, true);
        request.responseType = 'arraybuffer';
        request.onreadystatechange=function() {
            if (request.readyState === 4) {
                if (request.status === 200) {
                    that.ready = true;
                } else {
                    that.loadFailed = true;
                }
            }
        };
        request.onload = function() {
            var audioData = request.response;
            //解码
            that.audioContext.decodeAudioData(audioData, function(buffer) {
                        that.source.buffer = buffer;
//                        console.log(buffer.duration);//资源长度
//                        that.source.connect(that.audioContext.destination);
                        //将audioBufferSouceNode连接到audioContext.destination，
                        // 这个AudioContext的destination也就相关于speaker（扬声器）。
                        that.source.loop = that.config.loop||false;

                    },
                    function(e){"Error with decoding audio data" + e.err});
        };
        request.send();
    },
    play: function () {
        var that = this;
        that.source.start(0);
        that.playing = true;
        var timer = setInterval(function () {
            that.analyser.getByteFrequencyData(that.frequency);
            if (that.source.buffer){
                if (that.audioContext.currentTime>that.source.buffer.duration){
                    that.source.stop(0);
                    that.playing = false;
                    clearInterval(timer);
                }
            }
        },100);
    },
    stop: function () {
        var that = this;
        that.source.stop(0);
        that.playing = false;
    }
};

调用方法：

var v=new Visualizer({
    url:"2.mp3",//audio地址 没有写兼容跨域的方法，所以不能跨域
    loop:false//是否循环
});
v.init();
v.play();
setInterval(function () {
    if(v.ready){
          console.log("ready!");
    } else if(v.loadFailed){
          console.log("加载失败");
    }
    if (v.playing){ //playing判断是否在播放
        console.log(v.frequency);//frequency是长度为16的频率值数组
    }
},100);