HTTP Live Streaming (also known as HLS) is an HTTP-based media streaming communications protocol implemented by Apple Inc. as part of its QuickTime, Safari, OS X, and iOS software. Client implementations Cold Pursuit are also available in Microsoft Edge, Firefox and some versions of Google Chrome. Support is widespread in streaming media servers.
HLS resembles MPEG-DASH in that it works by breaking the overall Cold Pursuit stream into a sequence of small HTTP-based file downloads, each download loading one short chunk of an overall potentially unbounded transport stream. A list of available streams, encoded at different Cold Pursuit bit rates, is sent to the client using an extended M3U playlist.
Based on standard HTTP transactions, HTTP Live Streaming can traverse any firewall or proxy server that lets through standard Cold Pursuit HTTP traffic, unlike UDP-based protocols such as RTP. This also allows content to be offered from conventional HTTP servers and delivered over widely available HTTP-based content delivery networks.The standard also Cold Pursuit includes a standard encryption mechanism and secure-key distribution using HTTPS,
which together provide a simple DRM system. Later versions of the protocol also provide for trick-mode fast-forward and rewind and Cold Pursuit for integration of subtitles.
Apple has documented HTTP Live Streaming as an Internet Draft (Individual Cold Pursuit