Media Source Extensions
Video players (YouTube, Netflix, Twitch) use MSE for adaptive streaming. Required if you build a custom media player or do in-browser video processing.
What It Defines
W3C spec extending HTMLMediaElement to allow JavaScript to supply media segments dynamically. Enables adaptive bitrate streaming (HLS, DASH), live streams, and DVR-style seeks in browsers.
Canonical (Normative)
Convenient (Practical)
Publishes web platform specs including CSS, accessibility, security policies, Service Workers, Web App Manifest, and many browser APIs. Also maintains some versioned HTML/DOM specs.
Related Specs
Required for any platform that distributes premium or licensed video content (streaming services, pay-per-view, licensed media).
The spec behind every HTML page, form, and browser API. The canonical reference for how browsers actually parse and process HTML.