js 利用canvas + flv.js实现视频流 截屏 、本地下载功能实现，兼容火狐，谷歌；canvas截屏跨域问题，无音频视频流加载不显示问题
项目：物联网监控项目----后台视频流管理（前端实现视频截屏功能）
本文就不同视频源分情况展示:
1 本地视频(项目同目录视频)截屏（canvas.getContext("2d).drawImage()）
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title></title>
<link rel="stylesheet" href="">
<style type="text/css">
.screen_shot_btn,.screen_save_btn{display: inline-block;width: 72px;height: 36px;text-align: center;line-height: 36px;text-decoration: none;background: #4473C2;border: none;border-radius: 8px;margin:0 5px;color:#fff;outline: none;}
.btn-wrap{margin:15px 0;}
.img_show_wrap{width: 720px;height: 450px;margin:15px 0;position:relative;}
#image_el,#V2I_canvas{position:absolute;width: 720px;height: 450px;top:0;left:0;}
</style>
</head>
<body>
<div class="btn-wrap">
<a id="screen_shot_btn" class="screen_shot_btn" href="javascript:">截图</a>
<a id="screen_save_btn" class="screen_save_btn" href="javascript:">下载</a>
</div>
<div class="video_wrap">
<video id="video_el" autoplay width="720" height="450"><source src="images/sp.mp4" /></video>
</div>
<div class="img_show_wrap">
<canvas width="720" height="450" id="V2I_canvas" ></canvas>
<img id="image_el" src="" alt="">
</div>
<script src="js/jquery-1.11.3.min.js" type="text/javascript"></script>
<script type="text/javascript" src="js/flv.js"></script>
<script type="text/javascript">
$(function() {
var mySrc = "";
function htmlToImage() {
var canvas = document.getElementById("V2I_canvas");
if (!canvas.getContext) {
alert("您的浏览器暂不支持canvas");
return false;
} else {
var context = canvas.getContext("2d");
var video = document.getElementById("video_el");
context.drawImage(video, 0, 0, canvas.width, canvas.height);
return mySrc = canvas.toDataURL("image/png");
}
}
$("#screen_shot_btn").click(function(event) {
htmlToImage();
$("#image_el").attr("src", mySrc);
});
$("#screen_save_btn").click(function() {
htmlToImage();
if ($("#image_el").attr("src") != "") {
downloadFile(mySrc);
} else {
alert("内容为空");
}
})
function downloadFile(src) {
var triggerDownload = $("#screen_save_btn").attr("href", src).attr("download", "jietu.png");
}
})
</script>
</body>
</html>
2跨域视频截屏
note: 在video 标签内 添加 crossorigin="*" 即可
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title></title>
<link rel="stylesheet" href="">
<style type="text/css">
.screen_shot_btn,.screen_save_btn{display: inline-block;width: 72px;height: 36px;text-align: center;line-height: 36px;text-decoration: none;background: #4473C2;border: none;border-radius: 8px;margin:0 5px;color:#fff;outline: none;}
.btn-wrap{margin:15px 0;}
.img_show_wrap{width: 720px;height: 450px;margin:15px 0;position:relative;}
#image_el,#V2I_canvas{position:absolute;width: 720px;height: 450px;top:0;left:0;}
</style>
</head>
<body>
<div class="btn-wrap">
<a id="screen_shot_btn" class="screen_shot_btn" href="javascript:">截图</a>
<a id="screen_save_btn" class="screen_save_btn" href="javascript:">下载</a>
</div>
<div class="video_wrap">
<video id="video_el" crossorigin="*" autoplay width="720" height="450"><source src="http://jq22com.qiniudn.com/jq22-sp.mp4" /></video>
</div>
<div class="img_show_wrap">
<canvas width="720" height="450" id="V2I_canvas" ></canvas>
<img id="image_el" src="" alt="">
</div>
<script src="js/jquery-1.11.3.min.js" type="text/javascript"></script>
<script type="text/javascript" src="js/flv.js"></script>
<script type="text/javascript">
$(function() {
var mySrc = "";
function htmlToImage() {
var canvas = document.getElementById("V2I_canvas");
if (!canvas.getContext) {
alert("您的浏览器暂不支持canvas");
return false;
} else {
var context = canvas.getContext("2d");
var video = document.getElementById("video_el");
context.drawImage(video, 0, 0, canvas.width, canvas.height);
return mySrc = canvas.toDataURL("image/png");
}
}
$("#screen_shot_btn").click(function(event) {
htmlToImage();
$("#image_el").attr("src", mySrc);
});
$("#screen_save_btn").click(function() {
htmlToImage();
if ($("#image_el").attr("src") != "") {
downloadFile(mySrc);
} else {
alert("内容为空");
}
})
function downloadFile(src) {
var triggerDownload = $("#screen_save_btn").attr("href", src).attr("download", "jietu.png");
}
})
</script>
</body>
</html>
3 flv.js 实现 视频流截屏
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title></title>
<link rel="stylesheet" href="">
<style type="text/css">
.screen_shot_btn,.screen_save_btn{display: inline-block;width: 72px;height: 36px;text-align: center;line-height: 36px;text-decoration: none;background: #4473C2;border: none;border-radius: 8px;margin:0 5px;color:#fff;outline: none;}
.btn-wrap{margin:15px 0;}
.img_show_wrap{width: 720px;height: 450px;margin:15px 0;position:relative;}
#image_el,#V2I_canvas{position:absolute;width: 720px;height: 450px;top:0;left:0;}
</style>
</head>
<body>
<div class="btn-wrap">
<a id="screen_shot_btn" class="screen_shot_btn" href="javascript:">截图</a>
<a id="screen_save_btn" class="screen_save_btn" href="javascript:">下载</a>
</div>
<div class="video_wrap">
<video id="video_el" crossorigin="*" width="720" height="450"></video>
</div>
<div class="img_show_wrap">
<canvas width="720" height="450" id="V2I_canvas" ></canvas>
<img id="image_el" src="" alt="">
</div>
<script src="js/jquery-1.11.3.min.js" type="text/javascript"></script>
<script type="text/javascript" src="js/flv.js"></script>
<script type="text/javascript">
$(function() {
if (flvjs.isSupported()) {
var videoElement = document.getElementById('video_el');
var flvPlayer = flvjs.createPlayer({
type: 'flv',
url: 'http://192.168.30.218:8100/movie1'
});
flvPlayer.attachMediaElement(video_el);
flvPlayer.load();
flvPlayer.play();
}
var mySrc = "";
function htmlToImage() {
var canvas = document.getElementById("V2I_canvas");
if (!canvas.getContext) {
alert("您的浏览器暂不支持canvas");
return false;
} else {
var context = canvas.getContext("2d");
var video = document.getElementById("video_el");
context.drawImage(video, 0, 0, canvas.width, canvas.height);
return mySrc = canvas.toDataURL("image/png");
}
}
$("#screen_shot_btn").click(function(event) {
htmlToImage();
$("#image_el").attr("src", mySrc);
});
$("#screen_save_btn").click(function() {
htmlToImage();
if ($("#image_el").attr("src") != "") {
downloadFile(mySrc);
} else {
alert("内容为空");
}
})
function downloadFile(src) {
var triggerDownload = $("#screen_save_btn").attr("href", src).attr("download", "jietu.png");
}
})
</script>
</body>
</html>
总结：
1、 context.drawImage(image, 0, 0, canvas.width, canvas.height);
此处的 context.drawImage 的方法 video 应该为 image绘制到上下文的元素。允许任何的 canvas 图像源(CanvasImageSource)，例如：HTMLImageElement，HTMLVideoElement，或者 HTMLCanvasElement。
传送门：CanvasRenderingContext2D.drawImage() 。
note: 因此 视频流截屏时不能用 video.js ，因为video.js 本质是用的flash ,把video标签处理了.
2、出现跨域 不能用canvas.toDataURL（）
解决办法：1、把视频资源放入目录中
2，或者在 视频标签中添加 crossorigin="*"
3、 flv.js兼容性不大好，目前只测兼容pc 端火狐，谷歌；移动端不支持。下载的 download 属性兼容性 也不乐观，后续找到解决方案再补上。
4、 视频流如果无音频 可在属性里添加 hasAudio:false
无音频的话会出现，视频流加载进来但是无法播放的问题，控制台也不报错
-------------------------完-------------------------
---------------------（题外话）下载方法补充：-------------------------
借助 bolb download下载文件方法 替换上述 downloadFile方法（转自 by zhangxinxu from http://www.zhangxinxu.com/wordpress/?p=6252）：
图片下载方法：
var funDownload = function(domImg, filename) {
// 创建隐藏的可下载链接
var eleLink = document.createElement('a');
eleLink.download = filename;
eleLink.style.display = 'none';
// 图片转base64地址
var canvas = document.createElement('canvas');
var width = domImg.naturalWidth;
var height = domImg.naturalHeight;
canvas.width = width;
canvas.height = height;
var context = canvas.getContext('2d');
console.log(`${width}+${height}`);
context.drawImage(domImg, 0, 0,width,height);
// 如果是PNG图片，则context.toDataURL('image/png')
eleLink.href = canvas.toDataURL('image/png');
// 触发点击
document.body.appendChild(eleLink);
eleLink.click();
// 然后移除
document.body.removeChild(eleLink);
};
-----------------------------------------------------------
文本类 文件下载：
var fileDownload = function (content, filename) {
// 创建隐藏的可下载链接
var elLink = document.createElement('a');
elLink.download = filename;
elLink.style.display = 'none';
// 字符内容转变成blob地址
var blob = new Blob([content]);
elLink.href = URL.createObjectURL(blob);
// 触发点击
document.body.appendChild(elLink);
elLink.click();
// 然后移除
document.body.removeChild(elLink);
};
----------------------------------------
