canvas绘制视频封面的方法
一、需求：上传视频，同时截取视频某一帧作为视频的封面。
二、实现思路：利用canvas绘制图像的功能，绘制图像某一帧，这里绘制了第一帧，很简单就实现了。
三、代码：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>capture screen</title>
<style type="text/css">
video,#container{width: 300px;height: 200px;}
#container>img{width: 100%;}
</style>
</head>
<body>
<video id="video" controls="controls">
<source src="video/video_test.mp4">
</video>
<div id="container"></div>
<script type="text/javascript">
(function() {
var video, container;
var scale = 0.8;
var initialize = function() {
container = document.getElementById("container");
video = document.getElementById("video");
video.addEventListener('loadeddata', captureImage);
};
var captureImage = function() {
var canvas = document.createElement("canvas");
canvas.width = video.videoWidth * scale;
canvas.height = video.videoHeight * scale;
canvas.getContext('2d').drawImage(video, 0, 0, canvas.width, canvas.height);
var img = document.createElement("img");
img.src = canvas.toDataURL("image/png");//转换成base64图片，地址拿出来就可以直接使用
container.appendChild(img);
};
initialize();
})();
</script>
</body>
</html>
