JavaScript调用摄像头并截图预览的实现方法

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>摄像头调用实例</title>
<script type="text/javascript" src="jquery-3.2.1.min.js"></script>
<script type="text/javascript">
 var video, mediaStreamTrack, canvas;//声明全局变量
 //打开摄像头
 function dk() {
  video = document.getElementById("v1");
  var videoObj = {
   "video" : true
  };
  var errBack = function(error) {
   console.log("Video capture error: ", error.code);
  };
  //根据浏览器的不同选取不同的支持
  if (navigator.getUserMedia) { // Standarda
   navigator.getUserMedia(videoObj, function(stream) {
    mediaStreamTrack = typeof stream.stop === 'function' ? stream
      : stream.getTracks()[1];
    video.src = stream;//获取摄像头抓取的到字节流
    video.play();//实时播放摄像头
   }, errBack);
  } else if (navigator.webkitGetUserMedia) { // WebKit-prefixed
   navigator.webkitGetUserMedia(videoObj, function(stream) {
    mediaStreamTrack = typeof stream.stop === 'function' ? stream
      : stream.getTracks()[1];
    video.src = window.webkitURL.createObjectURL(stream);
    video.play();
   }, errBack);
  } else if (navigator.mozGetUserMedia) { // Firefox-prefixed
   navigator.mozGetUserMedia(videoObj, function(stream) {
    mediaStreamTrack = typeof stream.stop === 'function' ? stream
      : stream.getTracks()[1];
    video.src = window.URL.createObjectURL(stream);
    video.play();
   }, errBack);
  }
 }
 //截图
 function jq() {
  canvas = document.getElementById("c1");
  var context = canvas.getContext("2d");
  //将视频当前的页面转换为图片，显示到画板中
  context.drawImage(video, 0, 0, 200, 202);
  //把canvas图像转为img图片
  /* var src = canvas.toDataURL("image/jpeg");
  createImg(src); */
 }
 //关闭摄像头
 function gb() {
  mediaStreamTrack.stop();
 }
 //生成图片
 /* function createImg(src) {
  var dv = document.getElementById("dv1");
  var img = document.createElement("img");
  img.setAttribute("src", src);
  img.setAttribute("width", 205);
  img.setAttribute("height", 205);
  dv.appendChild(img);
 } */
 //上传
 /* function sc() {
  $.post('TestServlet', {
   "img" : canvas.toDataURL().substr(22)
  }, function(data, status) {
   alert(status != "success" ? "图片处理出错！" : data == "yes" ? "图片上传完成！"
     : data);
  });
 } */
</script>
<style type="text/css">
input[type="button"]{
border: 1px solid red;
}
</style>
</head>
<body>
 <div>
  <input type="button" value="打开" onclick="dk()"> 
  <input type="button" value="截取图像" onclick="jq()"> 
  <input type="button" value="关闭" onclick="gb()">
 </div>
 <div>
  <!--视频 -->
  <video width="200px" height="200px" id="v1"></video>
  <br />
  <!--画板 -->
  <canvas id="c1"></canvas>
  <br />
 </div>
 <!--记录每次截图的结果 -->
 <!-- <div id="dv1"></div> -->
</body>
</html>