详解js获取video任意时间的画面截图

<div contenteditable="true" id="in-box" style="width:1000px;margin: 20px auto;"></div>
<div style="width:1000px;margin: 20px auto;">  
 <input type="file" name="" id="upload-ipt">
 <div class="review" id="out-box"></div>
</div>

function getVideoImage() {
 var obj_file = document.getElementById("upload-ipt");
 var file = obj_file.files[0];
 var blob = new Blob([file]), // 文件转化成二进制文件
  url = URL.createObjectURL(blob); //转化成url
 if (file && /video/g.test(file.type)) {
  var $video = $('<div><video controls src="' + url + '"></video></div><div>&nbsp;</div>');
  //后面加一个空格div是为了解决在富文本中按Backspace时删除无反应的问题
  $('#in-box').html($video);
  var videoElement = $("video")[0];
  videoElement.addEventListener("canplay", function (_event) {
   var canvas = document.createElement("canvas");     
   canvas.width = videoElement.videoWidth;
   canvas.height = videoElement.videoHeight;
   console.log(videoElement.videoWidth)
   canvas.getContext('2d').drawImage(videoElement, 0, 0, canvas.width, canvas.height);
   var img = document.createElement("img");
   img.src = canvas.toDataURL("image/png");
   $("#out-box").html(img);
   URL.revokeObjectURL(this.src); // 释放createObjectURL创建的对象
   console.log("loadedmetadata")
  });
 }else{
  alert("请上传一个视频文件！");
  obj_file.value = ""
 }
};