HESP was published by THEO Technologies in 2019 and formalised as an HTTP-based alternative to LL-HLS, LL-DASH and WebRTC for sub-second live. The trick is splitting the stream in two: an "initialisation stream" of independently-decodable frames (every frame is a keyframe or close), used only for instant tune-in, and a "continuation stream" of compressed inter-frame video, used for normal playback. The player joins by pulling the latest init frame plus the continuation, achieving instant-on without the wait of a normal keyframe interval.
The architectural appeal is that HESP keeps HTTP semantics — segments can be cached on any HTTP CDN — while giving sub-second glass-to-glass latency comparable to WebRTC. Compared to LL-HLS, HESP usually clocks 500–800 ms vs LL-HLS's 2–4 s. Compared to WebRTC, HESP keeps the cache-friendly economics and avoids ICE/STUN/TURN entirely. The catch: HESP requires HESP-aware players and packagers, and the industry never fully embraced it as a standard.
HESP's footprint in 2026 is modest. THEO ships HESP as part of their player and packager; a few sports betting and casino-streaming operators use it. The broader market converged on LL-HLS and LL-DASH for medium-latency and WebRTC/MoQ for sub-second, leaving HESP in a niche. The technical ideas — split init/continuation streams, instant tune-in — have influenced the design of Media over QUIC.
