HTML5 中捕捉视频的小TIPS

今天发现一段不错的HTML 5小TIPS,主要是在支持HTML 5的浏览器上,
在播放视频时,可以点按钮,而把当前帧的图象CUT到一个canvas中去,下面上代码:

var videoId = 'video';
var scaleFactor = 0.25;
var snapshots = [];
 
/**
 * Captures a image frame from the provided video element.
 *
 * @param {Video} video HTML5 video element from where the image frame will be captured.
 * @param {Number} scaleFactor Factor to scale the canvas element that will be return. This is an optional parameter.
 *
 * @return {Canvas}
 */
function capture(video, scaleFactor) {
	if(scaleFactor == null){
		scaleFactor = 1;
	}
	var w = video.videoWidth * scaleFactor;
	var h = video.videoHeight * scaleFactor;
	var canvas = document.createElement('canvas');
		canvas.width  = w;
		canvas.height = h;
	var ctx = canvas.getContext('2d');
		ctx.drawImage(video, 0, 0, w, h);
	return canvas;
}
 
 
/**
 * Invokes the <code>capture</code> function and attaches the canvas element to the DOM.
 */
function shoot(){
	var video  = document.getElementById(videoId);
	var output = document.getElementById('output');
	var canvas = capture(video, scaleFactor);
		canvas.onclick = function(){
			window.open(this.toDataURL());
		};
	snapshots.unshift(canvas);
	output.innerHTML = '';
	for(var i=0; i<4; i++){
		output.appendChild(snapshots[i]);
	}
}

HTML 部分代码:

[align=center;]
	<video id="video" width="320" controls="true">
		<source src="video.ogv"><!-- FireFox 3.5 -->
		<source src="movie.mp4"><!-- WebKit -->
		Your browser does not support HTML5 video tag. Please download FireFox 3.5 or higher.
	</video><br/>
	<button onclick="shoot()" style="width: 64px;border: solid 2px #ccc;">Capture</button><br/>
	<div id="output" style="display: inline-block; top: 4px; position: relative ;border: dotted 1px #ccc; padding: 2px;">[/align]
</div>

样例在:http://appcropolis.com/blog/using-html5-canvas-to-capture-frames-from-a-video/