hls

HLS, short for HTTP Live Streaming, is a media streaming protocol developed by Apple for delivering audiovisual content over HTTP. It is designed to work with standard web servers and networks, enabling adaptive streaming for both live and on-demand content. HLS has become widely adopted in the industry and is supported by a range of devices and browsers, often through third-party players on non-Apple platforms.

The core idea behind HLS is to break a media stream into small, HTTP-accessible segments and to provide one or more playlists that describe those segments. A master playlist lists multiple variant playlists, each corresponding to a different bitrate and sometimes resolution. Each variant playlist then references a sequence of media segments, typically 2 to 10 seconds long. The client can switch between variants at segment boundaries to adapt to changing network conditions.

Content can be delivered using MPEG-TS segments or fragmented MP4 (fMP4) segments, with the latter becoming more common in modern deployments, especially with CMAF (Common Media Application Format). HLS supports encryption and content protection, using AES-128 for TS segments and, in CMAF-based workflows, broader DRM schemes via Common Encryption.

Delivery over standard HTTP simplifies scaling and firewall traversal and enables widespread caching by CDNs. Native support is strongest on Apple devices, while other platforms rely on media players that implement HLS, such as hls.js, or browser capabilities via Media Source Extensions.

HLS is formalized in IETF RFC 8216 and continues to evolve with extensions for low-latency streaming, multiple codecs, and interoperability with DRM technologies, maintaining its role as a foundational protocol for online video delivery.