js截屏 video_js获取视频截图

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

视频第一帧图片：

(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();

})();