HLS.js is a JavaScript library that 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. Transmuxing is performed asynchronously using a Web Worker when available in the browser. HLS.js also supports HLS + fmp4, as announced during WWDC2016.

HLS.js 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 Babel and the TypeScript compiler.

Rollup is used to build the distro bundle and serve the local development environment.

Features

• VOD & Live playlists
  • DVR support on Live playlists
• Fragmented MP4 container
• MPEG-2 TS container
  • ITU-T Rec. H.264 and ISO/IEC 14496-10 Elementary Stream
  • ITU-T Rec. H.265 and ISO/IEC 23008-2 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
  • ATSC A/52 / AC-3 / Dolby Digital 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 (ID3 format carried in MPEG-2 TS, Emsg in CMAF/Fragmented MP4, and DATERANGE playlist tags)
• AES-128 decryption
• "identity" format SAMPLE-AES decryption of MPEG-2 TS segments only
• Encrypted media extensions (EME) support for DRM (digital rights management)
  • FairPlay, PlayReady, Widevine CDMs with fmp4 segments
• Level capping based on HTMLMediaElement resolution, dropped-frames, and HDCP-Level
• 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
  • All internal events can be monitored (Network Events, Video Events)
  • Playback session metrics are also exposed
• Resilience to errors
  • Retry mechanism embedded in the library
  • Recovery actions can be triggered fix fatal media or network errors
• Redundant/Failover Playlists
• HLS Variable Substitution

Supported HLS tags

For details on the HLS format and these tags' meanings, see https://datatracker.ietf.org/doc/html/draft-pantos-hls-rfc8216bis

Multivariant Playlist tags

• #EXT-X-STREAM-INF:<attribute-list> <URI>
• #EXT-X-MEDIA:<attribute-list>
• #EXT-X-SESSION-DATA:<attribute-list>
• #EXT-X-SESSION-KEY:<attribute-list> EME Key-System selection and preloading
• #EXT-X-START:TIME-OFFSET=<n>
• #EXT-X-CONTENT-STEERING:<attribute-list> Content Steering
• #EXT-X-DEFINE:<attribute-list> Variable Substitution (NAME,VALUE,QUERYPARAM attributes)

Media Playlist tags

• #EXTM3U (ignored)
• #EXT-X-INDEPENDENT-SEGMENTS (ignored)
• #EXT-X-VERSION=<n> (value is ignored)
• #EXTINF:<duration>,[<title>]
• #EXT-X-ENDLIST
• #EXT-X-MEDIA-SEQUENCE=<n>
• #EXT-X-TARGETDURATION=<n>
• #EXT-X-DISCONTINUITY
• #EXT-X-DISCONTINUITY-SEQUENCE=<n>
• #EXT-X-BITRATE
• #EXT-X-BYTERANGE=<n>[@<o>]
• #EXT-X-MAP:<attribute-list>
• #EXT-X-KEY:<attribute-list> (KEYFORMAT="identity",METHOD=SAMPLE-AES is only supports with MPEG-2 TS segments)
• #EXT-X-PROGRAM-DATE-TIME:<attribute-list>
• #EXT-X-START:TIME-OFFSET=<n>
• #EXT-X-SERVER-CONTROL:<attribute-list>
• #EXT-X-PART-INF:PART-TARGET=<n>
• #EXT-X-PART:<attribute-list>
• #EXT-X-SKIP:<attribute-list> Delta Playlists
• #EXT-X-RENDITION-REPORT:<attribute-list>
• #EXT-X-DATERANGE:<attribute-list> Metadata
  • HLS EXT-X-DATERANGE Schema for Interstitials
• #EXT-X-DEFINE:<attribute-list> Variable Import and Substitution (NAME,VALUE,IMPORT,QUERYPARAM attributes)
• #EXT-X-GAP (Skips loading GAP segments and parts. Skips playback of unbuffered program containing only GAP content and no suitable alternates. See #2940)

Parsed but missing feature support:

• #EXT-X-PRELOAD-HINT:<attribute-list> (See #5074)
  • #5074

Not Supported

For a complete list of issues, see "Top priorities" in the Release Planning and Backlog project tab. Codec support is dependent on the runtime environment (for example, not all browsers on the same OS support HEVC).

• #EXT-X-I-FRAME-STREAM-INF I-frame Media Playlist files
• REQ-VIDEO-LAYOUT is not used in variant filtering or selection
• "identity" format SAMPLE-AES method keys with fmp4, aac, mp3, vtt... segments (MPEG-2 TS only)
• MPEG-2 TS segments with FairPlay Streaming, PlayReady, or Widevine encryption
• FairPlay Streaming legacy keys (For com.apple.fps.1_0 use native Safari playback)
• MP3 elementary stream audio in IE and Edge (<=18) on Windows 10 (See #1641 and Microsoft answers forum)

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

You can safely require this library in Node and absolutely nothing will happen. A dummy object is exported so that requiring the library does not throw an error. HLS.js is not instantiable in Node.js. See #1841 for more details.

Getting started with development

First, checkout the repository and install the required dependencies

git clone https://github.com/video-dev/hls.js.git
cd hls.js
# After cloning or pulling from the repository, make sure all dependencies are up-to-date
npm install ci
# Run dev-server for demo page (recompiles on file-watch, but doesn't write to actual dist fs artifacts)
npm run dev
# After making changes run the sanity-check task to verify all checks before committing changes
npm run sanity-check

The dev server will host files on port 8000. Once started, the demo can be found running at http://localhost:8000/demo/.

Before submitting a PR, please see our contribution guidelines. Join the discussion on Slack via video-dev.org in #hlsjs for updates and questions about development.

Build tasks

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

npm install ci
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 - 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.

NOTE: hls.light.*.js dist files do not include alternate-audio, subtitles, CMCD, EME (DRM), or Variable Substitution support. In addition, the following types are not available in the light build:

• AudioStreamController
• AudioTrackController
• CuesInterface
• EMEController
• SubtitleStreamController
• SubtitleTrackController
• TimelineController
• CmcdController

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

Formatting Code

Run prettier to format code

npm run prettier

Type Check

Run type-check to verify TypeScript types

np