JavaScript HLS client using Media Source Extension Saturday, Dec 19, 2020


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Join the discussion via in #hlsjs (our Slack channel)


hls.js is a JavaScript library which implements an HTTP Live Streaming client. It relies on HTML5 video and MediaSource Extensions for playback.

It works by transmuxing MPEG-2 Transport Stream and AAC/MP3 streams into ISO BMFF (MP4) fragments. This transmuxing could be performed asynchronously using Web Worker if available in the browser. hls.js also supports HLS + fmp4, as announced during WWDC2016

hls.js does not need any player, it works directly on top of a standard HTML<video>element.

hls.js is written in ECMAScript6 (*.js) and TypeScript (*.ts) (strongly typed superset of ES6), and transpiled in ECMAScript5 using the TypeScript compiler.

Modules written in TS and plain JS/ES6 can be interdependent and imported/required by each other.

To build our distro bundle and serve our development environment we use Webpack.

API docs and usage guide

Note you can access the docs for a particular version using “"


Latest Release


Specific Version

Find the commit on

Getting Started

<script src=""></script>
<!-- Or if you want a more recent alpha version -->
<!-- <script src=""></script> -->
<video id="video"></video>
  var video = document.getElementById('video');
  var videoSrc = '';
  if (Hls.isSupported()) {
    var hls = new Hls();
  // hls.js is not supported on platforms that do not have Media Source
  // Extensions (MSE) enabled.
  // When the browser has built-in HLS support (check using `canPlayType`),
  // we can provide an HLS manifest (i.e. .m3u8 URL) directly to the video
  // element through the `src` property. This is using the built-in support
  // of the plain video element, without using hls.js.
  // Note: it would be more normal to wait on the 'canplay' event below however
  // on Safari (where you are most likely to find built-in HLS support) the
  // video.src URL must be on the user-driven white-list before a 'canplay'
  // event will be emitted; the last video event that can be reliably
  // listened-for when the URL is not on the white-list is 'loadedmetadata'.
  else if (video.canPlayType('application/')) {
    video.src = videoSrc;

Alternative setup

Note that the example code above will check for hls.js support first and then fallback to check if the browser natively supports HLS. If you want to check for native browser support first, and then fallback to Hls.js you will want to swap those conditionals.

The order of these checks depends on if you want to use hls.js whenever possible see this comment to understand some of the tradeoffs.

<script src=""></script>
<!-- Or if you want a more recent alpha version -->
<!-- <script src=""></script> -->
<video id="video"></video>
  var video = document.getElementById('video');
  var videoSrc = '';
  // First check for native browser HLS support
  if (video.canPlayType('application/')) {
    video.src = videoSrc;
  // If no native HLS support, check if hls.js is supported
  } else if (Hls.isSupported()) {
    var hls = new Hls();

Video Control

Video is controlled through HTML <video> element.

HTMLVideoElement control and events could be used seamlessly.

They use hls.js in production!

Player Integration

hls.js is (being) integrated in the following players:

Chrome/Firefox integration

made by gramk, plays hls from address bar and m3u8 links


No external JS libs are needed. Prepackaged build is included with the releases.

If you want to bundle the application yourself, use node

npm install hls.js

or for the version from master (alpha)

npm install hls.js@alpha

NOTE: hls.light.*.js dist files do not include subtitling and alternate-audio features.


Either directly include dist/hls.js or dist/hls.min.js

Or type

npm install --save hls.js

Optionally there is a declaration file available to help with code completion and hinting within your IDE for the hls.js api

npm install --save-dev @types/hls.js


hls.js is compatible with browsers supporting MediaSource extensions (MSE) API with ‘video/MP4’ mimetypes inputs.

Find a support matrix of the MediaSource API here:

As of today, it is supported on:

  • Chrome for Android 34+
  • Chrome for Desktop 34+
  • Firefox for Android 41+
  • Firefox for Desktop 42+
  • IE11+ for Windows 8.1+
  • Edge for Windows 10+
  • Opera for Desktop
  • Vivaldi for Desktop
  • Safari for Mac 8+ (beta)

Please note: iOS Safari “Mobile” does not support the MediaSource API. Safari browsers have however built-in HLS support through the plain video “tag” source URL. See the example above (Getting Started) to run appropriate feature detection and choose between using Hls.js or natively built-in HLS support.

When a platform has neither MediaSource nor native HLS support, you will not be able to play HLS.

Server-side-rendering (SSR) and require from a Node.js runtime

We support this now. You can safely require this library in Node and absolutely nothing will happen :) See

(This is also known as “Universal builds” and “isomorphic apps”)


All HLS resources must be delivered with CORS headers permitting GET requests.


  • VoD & Live playlists
    • DVR support on Live playlists
  • fragmented MP4 container (beta)
  • MPEG-2 TS container
    • ITU-T Rec. H.264 and ISO/IEC 14496-10 Elementary Stream
    • ISO/IEC 13818-7 ADTS AAC Elementary Stream
    • ISO/IEC 11172-3 / ISO/IEC 13818-3 (MPEG-1/2 Audio Layer III) Elementary Stream
    • Packetized metadata (ID3v2.3.0) Elementary Stream
  • AAC container (audio only streams)
  • MPEG Audio container (MPEG-1/2 Audio Layer III audio only streams)
  • Timed Metadata for HTTP Live Streaming (in ID3 format, carried in MPEG-2 TS)
  • AES-128 decryption
  • SAMPLE-AES decryption (only supported if using MPEG-2 TS container)
  • Encrypted media extensions (EME) support for DRM (digital rights management)
    • Widevine CDM (beta/experimental) (see Shaka-package test-stream in demo)
  • CEA-608/708 captions
  • WebVTT subtitles
  • Alternate Audio Track Rendition (Master Playlist with alternative Audio) for VoD and Live playlists
  • Adaptive streaming
    • Manual & Auto Quality Switching
      • 3 Quality Switching modes are available (controllable through API means)
        • Instant switching (immediate quality switch at current video position)
        • Smooth switching (quality switch for next loaded fragment)
        • Bandwidth conservative switching (quality switch change for next loaded fragment, without flushing the buffer)
      • In Auto-Quality mode, emergency switch down in case bandwidth is suddenly dropping to minimize buffering.
  • Accurate Seeking on VoD & Live (not limited to fragment or keyframe boundary)
  • Ability to seek in buffer and back buffer without redownloading segments
  • Built-in Analytics
    • Every internal events could be monitored (Network Events,Video Events)
    • Playback session metrics are also exposed
  • Resilience to errors
    • Retry mechanism embedded in the library
    • Recovery actions could be triggered fix fatal media or network errors
  • Redundant/Failover Playlists

Not Supported (Yet)

  • MP3 Elementary Stream in Edge for Windows 10+

Supported M3U8 tags


hls.js is released under Apache 2.0 License

Development and contributing - first steps

Pull requests are welcome. Here is a quick guide on how to start.

  • First, checkout the repository and install required dependencies
git clone
# setup dev environment
cd hls.js
npm install
# runs dev-server for demo page (recompiles on file-watch, but doesn't write to actual dist fs artifacts)
npm run dev
# lint
npm run lint
  • Use EditorConfig or at least stay consistent to the file formats defined in the .editorconfig file.
  • Develop in a topic branch, not master
  • Don’t commit the updated dist/hls.js file in your PR. We’ll take care of generating an updated build right before releasing a new tagged version.


After cloning or pulling from the repository, first of all, make sure your local node-modules are up-to-date with the package deps:

npm install

Build system (Webpack)

Build all flavors (suitable for prod-mode/CI):

npm install
npm run build

Only debug-mode artifacts:

npm run build:debug

Build and watch (customized dev setups where you’ll want to host through another server than webpacks' - for example in a sub-module/project)

npm run build:watch

Only specific flavor (known configs are: debug, dist, light, light-dist, demo):

npm run build -- --env dist # replace "dist" by other configuration name, see above ^

Note: The “demo” config is always built.

Build with bundle analyzer (to help optimize build size)

npm run build:analyze

Linter (ESlint)

Run linter:

npm run lint

Run linter with auto-fix mode:

npm run lint:fix

Run linter with errors only (no warnings)

npm run lint:quiet

Automated tests (Mocha/Karma)

Run all tests at once:

npm test

Run unit tests:

npm run test:unit

Run unit tests in watch mode:

npm run test:unit:watch

Run functional (integration) tests:

npm run test:func


Click here for details.

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