step2.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>监控系统</title>
</head>
<body>
<video width="640" height="480" autoplay></video>
<canvas width="640" height="480"></canvas>

<script>
    var video = document.querySelector('video');
    var canvas = document.querySelector('canvas');

    // video捕获摄像头画面
    navigator.webkitGetUserMedia({
                video: true
            }, success, error);

    function success(stream) {
        video.src = window.webkitURL.createObjectURL(stream);
        video.play();
    }

    function error(err) {
        alert('video error: ' + err)
    }

    //canvas
    var context = canvas.getContext('2d');

    setTimeout(function(){
        //把当前视频帧内容渲染到画布上
        context.drawImage(video, 0, 0, 640, 480);
    }, 5000);

</script>
</body>
</html>