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].

[Webpack] is used to build the distro bundle and serve the local development environment.

[html5 video]: https://www.html5rocks.com/en/tutorials/video/basics/

[mediasource extensions]: https://w3c.github.io/media-source/

[http live streaming]: https://en.wikipedia.org/wiki/HTTP_Live_Streaming

[web worker]: https://caniuse.com/#search=worker

[ecmascript6]: https://github.com/ericdouglas/ES6-Learning#articles--tutorials

[typescript]: https://www.typescriptlang.org/

[typescript compiler]: https://www.typescriptlang.org/docs/handbook/compiler-options.html

[webpack]: https://webpack.js.org/

- 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

  - 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 (ID3 format carried in MPEG-2 TS, Emsg in CMAF/Fragmented MP4, and DATERANGE playlist tags)

- AES-128 decryption

- SAMPLE-AES decryption (only supported if using MPEG-2 TS container)

- Encrypted media extensions (EME) support for DRM (digital rights management)

  - FairPlay, PlayReady, Widevine CDMs with fmp4 segments

- 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

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