使用getUserMedia 调用摄像头

html5中一个有趣的 API，能够调用电脑的摄像头，结合 <video> 标签和 Canvas 就能在浏览器中拍摄照片了。

这里需要注意:

因为安全问题, chrome 对于本地文件禁用了很多功能(以file:///开头). 所以如果你直接把html文件拖进chrome是看不到效果的(getUserMedia 失败). 这个问题让我疑惑了挺久的.

解决办法:

1. 使用IDE 来查看效果, 比如webstorm.

2. 配合http服务器. 比如python simplehttpserver. 或者apache等等.

3. 关闭所有chrome窗口(否则参数无效). 在命令行中增加如下参数启动chrome.

chrome --allow-file-access-from-files

一个示例

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>

<p>Using Opera Next or Chrome Canary, use this page to take your picture!</p>


<video id="video" width="640" height="480" autoplay></video>
<button id="snap" class="sexyButton">Snap Photo</button>
<canvas id="canvas" width="640" height="480"></canvas>

<script>

    // Put event listeners into place
    window.addEventListener("DOMContentLoaded", function() {
        // Grab elements, create settings, etc.
        var canvas = document.getElementById("canvas"),
                context = canvas.getContext("2d"),
                video = document.getElementById("video"),
                videoObj = { "video": true },
                errBack = function(error) {
                    console.log("Video capture error: ", error.code);
                };

        // Put video listeners into place
        if(navigator.getUserMedia) { // Standard
            navigator.getUserMedia(videoObj, function(stream) {
                video.src = stream;
                video.play();
            }, errBack);
        } else if(navigator.webkitGetUserMedia) { // WebKit-prefixed
            navigator.webkitGetUserMedia(videoObj, function(stream){
                video.src = window.webkitURL.createObjectURL(stream);
                video.play();
            }, errBack);
        } else if(navigator.mozGetUserMedia) { // WebKit-prefixed
            navigator.mozGetUserMedia(videoObj, function(stream){
                video.src = window.URL.createObjectURL(stream);
                video.play();
            }, errBack);
        }

        // Trigger photo take
        document.getElementById("snap").addEventListener("click", function() {
            context.drawImage(video, 0, 0, 640, 480);
        });
    }, false);

</script>

</body>
</html>

　　代码参考自 http://davidwalsh.name/demo/camera.php