JS实现预加载视频音频/视频获取截图（返回canv

/**
 * Create by Capricorncd 2017
 */
// 同域资源实现视频截图，可上传的图片数据格式
// 非同域资源实现canvas截图预览
// 提示码
const CODES = {
 0: 'success',
 1: 'The url is not valid',
 2: 'onerror'
}
/**
 * constructor
 * @param opts.url 音频|视频URL
 * @param opts.type 'audio|video'
 * @param opts.callback 回调函数
 */
function loadMedia(opts) {
 this.callback = opts.callback || function (res) {
  console.log(res);
 }
 // 初始化
 this.init(opts);
}
// prototype
loadMedia.prototype = {
 /**
  * 初始化media
  * @param url
  */
 init: function (opts) {
  let self = this;
  if (!opts.url || typeof opts.url !== 'string') {
   this.callback({code: 1, msg: CODES[1]});
   return;
  }
  // 创建media
  let mediaType = opts.type === 'audio' ? 'audio' : 'video';
  this.media = document.createElement(mediaType);
  console.log('this.media', this.media);
  // loaded
  this.listener('canplaythrough', function (e) {
   // 截图
   if (mediaType === 'video') {
    self.screenshot();
   } else {
    self.callback({
     code: 0,
     msg: CODES[0],
     thumb: null,
     media: this.media,
     canvas: null
    });
   }
  });
  // error
  this.listener('error', function (e) {
   self.callback({code: 2, msg: CODES[2], data: e});
  })
  this.media.setAttribute('src', opts.url);
 },
 screenshot: function () {
  // create canvas
  let canvas = document.createElement('canvas');
    canvas.width = this.media.videoWidth;
    canvas.height = this.media.videoHeight;
  let ctx = canvas.getContext('2d');
  // 截取
  ctx.drawImage(this.media, 0, 0);
  let thumb = null;
  // 非跨域资源
  // !!非同域资源无法获取数据
  try {
   let type = 'image/png';
   let data = canvas.toDataURL(type);
   thumb = this.toBlobData(data, type);
  } catch (e) {}
  this.callback({
   code: 0,
   msg: CODES[0],
   thumb: thumb,
   media: this.media,
   canvas: canvas
  })
 },
 // 数据转换
 toBlobData: function (data, type) {
  // 获取base64数据
  // base64数据格式:
  // "data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEASABIAAD/2wBDAAkGB+wgHBgkIBwgKCgkLDRYPDQw//9k="
  data = window.atob(data.split(',')[1]);
  let ia = new Uint8Array(data.length);
  for (let i = 0; i < data.length; i++) {
   ia[i] = data.charCodeAt(i);
  };
  // canvas.toDataURL 返回的默认格式是 image/png
  return new Blob([ia], {type: type});
 },
 /**
  * addEventListener 事件监听
  * @param en EventName
  * @param callback
  */
 listener: function (en, callback) {
  this.media.addEventListener(en, function (e) {
   if (callback) {
    callback(e);
   } else {
    console.warn(this);
   }
  }, false);
 }
 /**
  * 资源是否跨域
  * @param url 资源地址
  * @returns {boolean}
  */
 // isCrossDomain: function (url) {
 //  let loc, host, protocol;
 //  loc = window.location;
 //  host = loc.host;
 //  protocol = loc.protocol;
 //  // 是否为http链接
 //  if (/(http|https):\/\//.test(url)) {
 //   if (url.indexOf(protocol + '//' + host) >= 0) {
 //    return false;
 //   } else {
 //    return true;
 //   }
 //  }
 //  // './xxx.mp4' '/xxx.mp4' 'xxx.mp4'
 //  return false;
 // }
}