HTML5 track captions not showing

Track tag is working when your content is served at a web server. Also don't forget to add a configuration that sets mime type as vtt file. Here is my example that works on IIS :

<video>
   <source src="video.mp4" type="video/mp4" />
   <track src="video.en.vtt" kind="subtitles" 
         label="English Subtitles" srclang="en" />
</video>

For IIS Web.Config File :

<configuration>
    <system.webServer>
      <staticContent>
        <remove fileExtension=".vtt" />
        <mimeMap fileExtension=".vtt" mimeType="text/vtt" />
      </staticContent>
    </system.webServer>
</configuration>

For Tomcat Server WEB-INF/web.xml file :

<web-app>
  <mime-mapping>
    <extension>vtt</extension>
    <mime-type>text/vtt</mime-type>
  </mime-mapping>
</web-app>

For Apache Server add .htaccess file to your web directory, and write that line to add subtitle mime type :

AddType text/vtt .vtt

You need to set the mode of the textTracks object to "showing":

var video = document.querySelector('YOUR_VIDEO_SELECTOR');

video.addEventListener('load', function() {
    var tracks = video.textTracks[0];
    tracks.mode = 'showing';
});

Make sure that your file is saved as UTF-8 to make sure that special characters will display properly

Canavar has the correct answer but one thing that worked for me was just to change the .vtt file to a .txt file, then you don't have to worried about the file server configuration. It handled the Closed Captioning just fine for me in Chrome.