How to get a preview of a video by its url?

Question

JavaScript

I'm not very familiar with canvas and apparently I'm doing something wrong.
I wanted to display a picture formed on the basis of src video. Here's how I tried

here is the code

res.media.src содержит путь к видео, проверял с ним все ок.

var canv = document.getElementById('video_can');             
                    var vid = document.getElementById('video_temp');    
                    vid.setAttribute('src', el.src);
                    var context = canv.getContext("2d");
                    context.drawImage(vid, 0, 0, 300,300);
                    var dataURL = canv.toDataURL();
                    console.log(dataURL);
                    res.media.src = $('<img src="'+dataURL+'">');

result in console

data:image/png;base64,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

This is the transparent area. What's wrong?

Answer 1

I found a problem, you have to wait until the video is loaded (at least the first frame) and all the manipulations must be done after that:

var v = document.createElement('video');
var canv = document.createElement('canvas');
v.setAttribute('src',el.src);
v.addEventListener('loadeddata',function() {
                        canv.setAttribute('height','300'); 
                        canv.setAttribute('width','300'); 
                        var context = canv.getContext("2d");
                        context.drawImage(this, 0, 0, 300,300);
                        var dataURL = canv.toDataURL();
}

So everything clearly worked, photo from shit, looks like shit. And if you wait until the first frame appears, then the first frame will appear accordingly.