EME (Encrypted Media Extensions) is the W3C browser API that wires a web player to a DRM system for protected playback. It is the standardized bridge between JavaScript and the browser's Content Decryption Module (CDM) — the component (Widevine in Chrome, PlayReady in Edge, FairPlay in Safari) that holds keys and decrypts media inside a protected boundary the page cannot peer into.
EME does not do encryption or define a DRM; it standardizes the handshake. The player detects that media is encrypted, EME asks the CDM for a license challenge, the player ships that challenge to the license server and returns the response to the CDM, and the CDM decrypts. This lets one player codebase support different DRMs across browsers through a common API.
EME works hand-in-hand with MSE (Media Source Extensions): MSE feeds the media segments for adaptive streaming, EME handles their decryption. Together they are what make DRM-protected adaptive playback possible in a browser without plugins.
