参考：
https://segmentfault.com/q/1010000006717959
问题：
a.获取的好像是第一帧的图？第一帧为透明图时，获取的个透明图片
b.得先加载视频到video,做视频上传的时候体验不太友好
c.qq空间能截取视频图片，不知道怎么实现的
<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <title></title> </head> <body> <video id="video" controls="controls" width="400" height="300"> <source src="myvideo.mp4"> </video> <br><br> 视频第一帧图片： <div id="output"></div> <script type="text/javascript"> (function(){ var video, output; var scale = 0.8; var initialize = function() { output = document.getElementById("output"); 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"); img.width = 400; img.height = 300; output.appendChild(img); }; initialize(); })(); </script> </body> </html>
原文：https://www.cnblogs.com/liuqiyun/p/9519842.html