Adding new website support

Adding new website support to H5VEW

With the recent rewrite of HTML5 Video EveryWhere extension to support the new WebExtension API. I decided to write a quick guide on how to add support for a new video streaming website. In this tutorial, I will document the steps followed to add support for

First, let's create a new module for this website. A HTML5 Video EveryWhere module is a subclass of Module class and it's injected into the web page containing the video player to replace. A module should at least override two functions:

  • The constructor() function to specify the module alias that it's used to identify different modules. The alias is hyphenated lowercased website name.
  • onInterative() function that is invoked when DOM is loaded (equivalent to the DOMContentLoaded event). This is the right place to write the needed code to change the site video player. Alternative functions that are available to override are onLoading and onComplete. onLoading will be invoked before parsing the DOM while onComplete will be invoked when the DOM and all the resources (images, subframes, ...) have been loaded.

So let's start with a minimal code that will print "Hello World" when injected into website. The module path will be content/Lego.js.

import Module from './Module.js';

class Lego extends Module {
  constructor() {
    // We overwrite the constructor to set the module name.

  onInteractive() {
    // Here we are using the Module `log` method.
    this.log("Hello World");

// Needed to execute the module on file injection
new Lego().start();

You will notice we are using ES6 Modules syntax. Even it's still not supported by the Firefox WebExtensions, it will transcompiled into Firefox v52+ valid code using babel at a later step. You can use all the fancy latest ES syntax without worring about the bowser support. You will notice the use of log function defined on Module class, it's a wrapper of console.log with namespacing the log message to identify the extension own messages, you should use it instead of direct using console API.

Now, we need this module to be injected when opening video player page. After inspecting the site, we notice that its videos are opened within an iFrame and are hosted under path where en-US could be changed to the user locale code. We need to match this URL and inject the required files when opened. In manifest.json file, we add the following object into content_scripts field:

  "matches": ["*/mediaplayer/video/*"],
  "js": [
  "all_frames": true,
  "run_at": "document_start"

First thing we notice is that besides content/Leog.js, we inject other files that are needed for the module to execute. These files are:

  • content/Modules.js: Defines Module class which is the parent class of all modules and contains common code and it's responsible to communique with the extension background script.
  • content/video-player.js: Defines VP class which creates the video player widget and add to it custom styles, properties based on the extension settings and also it adds a context menu to the video player.
  • content/statics.js: Tracks how often this module is used, browser/extension version and the browser default language.
  • content/common.js: Contains common functions used by more than when script.
  • content/Options.js: Defines Options class that contains all logic related to defining, retrieving and updating extension options. An instance of this class is created by Module class under the options attribute.

We can also notice that Lego video player is always hosted under the specified URL. All http:// requests are redirected to https:// protocol and all requests not containing the www resource are redirected to So our matching pattern is just one simple pattern.

Next, we need to define a new option to disable this module. In content/Options.js, add to defaults attribute in the constructor the new option which is of type boolean and with default value false.

this.defaults = {
  // ...
  disablelego: ["boolean", false],

To test our code, open about:debugging URL in Firefox and load the extension. You should see the "Hello World" message when you visit a web page with Lego.comm video player embed in.

Now, we can move forward by updating onIntercative function code to extract video URLs and replace the video player with an instance of VP. Generally, the module code logic follows these steps:

  • (Optional) Validate the URL of the document in case the matches patterns are not enough to eliminate pages URL which are known to not include the video player. Or to invoke different code for different URLs patterns. e.g: YouTube watch page vs. channels/users page.
  • Extract video data including video files path and poster URL. These data can be included inside the HTML document as JavaScript variable or as embed JSON document or as tag attributes. Or these data can be downloaded from other URL. In this case, you have to add the URL pattern of the resource to permissions field in the manifest.json file if it is hosted on a different domain.
  • Create an instance of VP class with the container element of the video player as first argument and this.options as second option.
  • Add video URLs using either VP.srcs() or VP.addSrc() methods. The first expects an object with the video quality/format as key and the video URL as value. The second method expects the video URL as first argument, the video quality as second argument (possible values: "low", "medium", "high" or "higher") and the video format as third argument (possible values: "mp4" or "webm").
  • Set the poster URL using VP.props() function which expects an object of the HTMLVideoElement attributes and its values. In this case, set poster attribute to the poster URL.
  • Invoke VP.setup() method to replace the website video player with the browser video player, to add video sources and to apply all provided styles and properties.

We resume. To add new website support. We implement a subclass of Module with overwriting one of its abstract methods but mostly onInterative. We add a new entry to the module with its matching URL patterns to content_scripts on manifest.json. We add module specific options definitions into defaults property of content/Options.js module. The final implementation of module can be found on HTML5 Video EveryWhere repository. I welcome patches for new websites support, for new language translation or for issue fixing.