cannot play webm file

[ghost]

I am trying to create a .webm file locally but when I try to play it it will not work.

  var fs = require('fs');
  window.name = 'popup';
  function onTabStream(stream) {
    window.web_stream = stream;
    var encodedStream = MediaStreamToWebm.EncodedStream(stream)
    var ws = fs.createWriteStream('sample.webm');
    encodedStream.pipe(ws); 
    
    document.getElementById('result').innerHTML = 'stream created. click the button on the main window. ';
  }
  chrome.tabCapture.capture({ audio: false, video: true }, onTabStream);