// 这是保存图片的函数。它模拟点击链接，打开保存窗口
function download(href, name) {
	var save_link = document.createElementNS('http://www.w3.org/1999/xhtml', 'a');
	save_link.href = href;
	save_link.download = name;
	var event = document.createEvent('MouseEvents');
	event.initMouseEvent('click', true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
	save_link.dispatchEvent(event);
}
// 获取页面的video元素
var v = document.querySelector('video');
// 创建canvas元素并绘制video元素内容
var c = document.createElement('canvas');
c.width = v.videoWidth;
c.height = v.videoHeight;
c.getContext('2d').drawImage(v, 0, 0, c.width, c.height);
// 绘制后，获取图片数据并下载
c.toBlob(function(b) {
	var u = URL.createObjectURL(b);
	download(u, '1.png');
	URL.revokeObjectURL(u);
});