Javascript store video

I am currently working on a Unity Webgl project and I am new to javascript and web .

In my project the user have to be able to add pictures and videos to the the webgl player, picture works fine (thanks to gman's code on this thread). I use it as a base for my scrip. Of course I have changed the input accept to be able to get video (mp4 only). But I am getting some trouble.

I have read this tutorial and all the doc I have found about javascript File, blob, etc. But I didn't make it work. I believe there is something I don't understand with FileReader since the console.log on the "load" listener is never called, same for the "onerror" listener except when I click on cancel (from the code here).

      function getPic(evt) {
    var file    = document.querySelector('input[type=file]').files[0];
    var reader  = new FileReader();

    reader.addEventListener("onload", function () {
        reader.readAsDataURL(file);
        console.log(reader.result);
    }, false);
    reader.addEventListener("onerror", function (error) {
        console.log("error" + error);
    }, false);
  }

I have tried onloadend too but it don't work, since the onload/onloadend listener is never called my script print "null". Is that a good beginning or is there a simpler way to get video/image from user computer ?