HLS Service Worker

Service Worker for HLS video prefetching

Architecture

Build

node build.js   # Concatenates src/ → sw.js

Demo

uv run python3 web.py

# Chrome: http://localhost:3001/webtest/

Test

node test_offline_startup.js

Key Features

• Progressive playlist parsing - Start playback before full manifest loads
• Lookahead prefetch - Preload segments ahead of playback position
• Multi-tier cache - Memory → Disk (Cache API) with quota enforcement
• Stall detection + range requests - Switch to parallel range fetches on slow downloads
• Recovery/cooldown - Retry with backoff, host/segment cooldown

Messages (Client → SW)

Type	Purpose
LINE_CHANGE	Reset state, send INITIAL to client
PREPARE_START	Parse manifest, prefetch target + lookahead
TIMELINE_JUMP	Set seek target time
PLAYER_STATE	isPaused, seeked
PLAYBACK_POSITION_UPDATE	Periodic position for adaptive prefetch

Messages (SW → Client)

Type	Purpose
INITIAL	Client should re-initialize
PREPARE_PROGRESS	Preparation progress %
PREPARE_START_READY	Target segment ready