html5调用手机摄像头

html:<video id="video" autoplay=""style=‘width:640px;height:480px‘></video><button id=‘picture‘>PICTURE</button><canvas id="canvas" width="640" height="480"></canvas></body>js:<script>    var video = document.getElementById("video");    var context = canvas.getContext("2d")    var errocb = function () {        console.log(‘sth wrong!‘);    }    if (navigator.getUserMedia) { // 标准的API        navigator.getUserMedia({ "video": true }, function (stream) {            video.src = stream;            video.play();        }, errocb);    } else if (navigator.webkitGetUserMedia) { // WebKit 核心的API        navigator.webkitGetUserMedia({ "video": true }, function (stream) {            video.src = window.webkitURL.createObjectURL(stream);            video.play();        }, errocb);    }    document.getElementById("picture").addEventListener("click", function () {        context.drawImage(video, 0, 0, 640, 480);    });

</script>