将html5视频的第一帧存储到没有ffmpeg的文件夹中

Question

I have a problem with fetching first frame of html5 video. i tried with canvas. here my code

var canvas = document.getElementById('canvas');
var video = document.getElementById('video');
canvas.getContext('2d').drawImage(video, 0, 0, video.videoWidth, video.videoHeight);
canvas.href = canvas.toDataURL();
canvas.download = "myimg.png";

i drawn the result. thats fine. but now my problem is i want to save result( that drawn image) directly into folder. Also i can't able to convert canvas image to URL format using DataURL()