Live DVR and time-shift

Design the DVR / time-shift and live-to-VOD system for a live event platform. While a stream is live, viewers must be able to pause, rewind, and seek backward to any earlier point in the broadcast (full DVR window), and the moment the stream ends the full recording must be available as on-demand VOD with seeking and chapters, ideally within seconds. A single event can be 12 hours long with millions of viewers. Design the segment storage, the manifest, and the live-to-VOD transition.