<!--video用于显示媒体设备的视频流，自动播放-->   
<video  id="video" autoplay style="width: 480px;height: 320px"></video>
<!--拍照按钮-->
<div>
    <button id="capture">拍照</button>
</div>
<!--描绘video截图-->
<canvas id="canvas" width="480" height="320"></canvas>

<script>  
    var video = document.getElementById('video');
    var canvas = document.getElementById('canvas');
    var capture = document.getElementById('capture');
    var context = canvas.getContext('2d');
    function getUserMediaToPhoto(constraints,success,error) {
        if(navigator.mediaDevices.getUserMedia){
            //最新标准API
            navigator.mediaDevices.getUserMedia(constraints).then(success).catch(error);
        }else if (navigator.webkitGetUserMedia) {
            //webkit核心浏览器
            navigator.webkitGetUserMedia(constraints,success,error);
        }else if(navigator.mozGetUserMedia){
            //firefox浏览器
            navigator.mozGetUserMedia(constraints,success,error);
        }else if(navigator.getUserMedia){
            //旧版API
            navigator.getUserMedia(constraints,success,error);
        }
    }
    //成功回调函数
    function success(stream){
        //兼容webkit核心浏览器
        var CompatibleURL = window.URL || window.webkitURL;
        //将视频流转化为video的源
        video.src = CompatibleURL.createObjectURL(stream);
        video.play();//播放视频
    }
    function error(error) {
        console.log('访问用户媒体失败：',error.name,error.message);
    }
    if(navigator.mediaDevices.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.getUserMedia){
        getUserMediaToPhoto({video:{width:480,height:320}},success,error);
    }else{
        alert('你的浏览器不支持访问用户媒体设备');
    }
    capture.addEventListener('click',function() {
        // 将video画面描绘在canvas画布上
        context.drawImage(video,0,0,480,320);
    })
 </script>