一般的视频网站对于用户上传的视频,在用户上传完成后,可以对播放的视频进行截图,然后作为视频的展示图。项目中也可以引入这样的功能给用户一种不错的体验,而不是让用户额外上传一张展示图。
效果图:
看起来还是很不错,下面我给大家分析下,极其核心代码很简单:
- _canvas = document.createElement("canvas");
- _ctx = _canvas.getContext("2d");
- _ctx.fillStyle = '#ffffff';
- _ctx.fillRect(0, 0, _videoWidth, _videoWidth);
- _ctx.drawImage(_video, 0, 0, _videoWidth, _videoHeight, 0, 0, _videoWidth, _videoHeight);
- var dataUrl = _canvas.toDataURL("image/png");
核心代码就这几行,利用了ctx.drawImage时,第一个参数可以为video对象,然后就是通过canvas拿到DataUrl,赋值给Img标签了。关键点就这些。
下面来看整个例子:
HTML:
- <!DOCTYPE html>
- <html>
- <head>
- <title></title>
- <meta charset="utf-8">
- <style type="text/css">
- html
- {
- overflow: hidden;
- }
- body
- {
- #999;
- }
- video
- {
- display: block;
- margin: 60px auto 0;
- }
- #shotBar
- {
- position: absolute;
- bottom: 5px;
- height: 120px;
- width: 98%;
- background-color: #000;
- box-shadow: -5px -5px 10px #fff;
- border-radius: 5px;
- padding: 2px;
- overflow: auto;
- }
- #shotBar img
- {
- border: 3px solid #fff;
- border-radius: 5px;
- height: 110px;
- width: 210px;
- margin-left: 4px;
- }
- </style>
- <script type="text/javascript" src="../../../jquery-1.8.3.js"></script>
- <script type="text/javascript" src="videoshot.js"></script>
- <script type="text/javascript">
- $(function ()
- {
- ZhangHongyang.click2shot.init();
- });
- </script>
- </head>
- <body>
- <video src="media/style.mp4" controls id="video">
- </video>
- <div id="shotBar">
- </div>
- </body>
- </html>
html和css都是相当简单的。
主要看Js的代码:
- /**
- * Created with JetBrains WebStorm.
- * User: zhy
- * Date: 14-6-18
- * Time: 上午12:24
- * To change this template use File | Settings | File Templates.
- */
- var ZhangHongyang = {};
- ZhangHongyang.click2shot = (function ()
- {
- var _ID_VIDEO = "video";
- var _ID_SHOTBAR = "shotBar";
- var _videoWidth = 0;
- var _videoHeight = 0;
- var _canvas = null;
- var _ctx = null;
- var _video = null;
- function _init()
- {
- _canvas = document.createElement("canvas");
- _ctx = _canvas.getContext("2d");
- _video = document.getElementById(_ID_VIDEO);
- _video.addEventListener("canplay", function ()
- {
- _canvas.width = _videoWidth = _video.videoWidth;
- _canvas.height = _videoHeight = _video.videoHeight;
- console.log(_videoWidth + " , " + _videoHeight);
- _ctx.fillStyle = '#ffffff';
- _ctx.fillRect(0, 0, _videoWidth, _videoWidth);
- $("#" + _ID_SHOTBAR).click(_click2shot);
- _video.removeEventListener("canplay", arguments.callee);
- });
- }
- function _click2shot(event)
- {
- _video.pause();
- _ctx.drawImage(_video, 0, 0, _videoWidth, _videoHeight, 0, 0, _videoWidth, _videoHeight);
- var dataUrl = _canvas.toDataURL("image/png");
- //创建一个和video相同位置的图片
- var $imgBig = $("<img/>");
- $imgBig.width(_videoWidth).height(_videoHeight).css({position: "absolute", left: _video.offsetLeft, top: _video.offsetTop, width: _videoWidth + "px", height: _videoWidth + "px"}).attr("src", dataUrl);
- $("body").append($imgBig);
- //创建缩略图,准备加到shotBar
- var $img = $("<img>");
- $img.attr("src", dataUrl);
- $(this).append($img);
- var offset = _getOffset($img[0]);
- $img.hide();
- //添加动画效果
- $imgBig.animate({left: offset.x + "px", top: offset.y + "px", width: $img.width() + "px", height: $img.height() + "px"}, 200, function ()
- {
- $img.attr("src", dataUrl).show();
- $imgBig.remove();
- _video.play();
- });
- }
- /**
- * 获取元素在显示区域的leftOffset和topOffset
- * @param elem
- * @returns {{x: (Number|number), y: (Number|number)}}
- * @private
- */
- function _getOffset(elem)
- {
- var pos = {x: elem.offsetLeft, y: elem.offsetTop};
- var offsetParent = elem.offsetParent;
- while (offsetParent)
- {
- pos.x += offsetParent.offsetLeft;
- pos.y += offsetParent.offsetTop;
- offsetParent = offsetParent.offsetParent;
- }
- return pos;
- }
- return {init: _init}
- })();
需要注意的是,video.canplay事件中获取完属性和一些操作后,一定要removeEventLinstener,否则暂停播放会一直调用此方
法。点击事件时,会暂停video,然后在video的位置生成一张图片,使用jquery动画移动到缩略图的位置,然后移除文档,缩略图显示,造成的动
画效果。
得到图片之后的上传之类的操作,大家可以自己添加。还有很重要的一点:canvas.toDataURL("image/png");可能需要在服务器中访问才能正常使用,我把写好的页面拖到了tomcat中,大家可以随便启动个什么服务器,不然会报安全问题。
From:http://blog.csdn.net/lmj623565791/article/details/31883587