Post
Record everything that happened in a match so anyone can watch it back from any angle like they are a virtual cameraman.
Replay systems record gameplay sessions so they can be played back later, typically for competitive review, content creation, or spectator features. There are two fundamental approaches: video capture (record pixel output) and input replay (record player inputs and re-simulate). Input replay is far more storage-efficient -- a 30-minute match might be a few kilobytes of input data versus gigabytes of video -- but requires a deterministic simulation to reproduce the exact same result. Many replay systems store both inputs and periodic state snapshots, allowing viewers to scrub to any point, switch camera angles, slow down or speed up playback, and follow different players. The engineering challenge is keeping the replay format stable across game patches so old replays remain watchable.
Example
Rocket League's replay system records all player inputs and physics states, allowing players to rewatch goals from any angle with a free-flying camera. The system became essential to the game's esports scene and content creator ecosystem, with highlight reels and coaching analyses all built from replay files.
Why it matters
Replay systems extend a game's value far beyond active play sessions. They enable esports analysis, content creation, coaching, anti-cheat review, and the viral highlight clips that drive community growth. For competitive games, a replay system is not a luxury feature -- it is infrastructure.
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