unity-replay-ghost

name	unity-replay-ghost
description	Unity Replay & Ghost System -- RC Racing

Unity Replay & Ghost System -- RC Racing

Use this skill when implementing replay recording, ghost car playback, lap ghost storage/sharing, or replay camera systems. Covers the full pipeline from state capture through compressed storage to interpolated playback with Cinemachine cameras.

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Table of Contents

1. Why State Recording, Not Input Recording
2. GhostFrame Struct
3. Recording Pipeline
4. Compression Pipeline
5. Storage Format
6. Ghost Playback
7. Ghost Visual Representation
8. Cinemachine Replay Cameras
9. Time Scrubbing
10. Async I/O
11. File Versioning
12. Anti-Cheat Validation
13. Networking and Distribution
14. Performance Budget
15. Testing Strategy

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1. Why State Recording, Not Input Recording

PhysX is non-deterministic across runs. Floating-point accumulation order varies with frame timing, thread scheduling, and solver iteration counts. Replaying the same input sequence produces divergent results within seconds -- unacceptable for a ghost that must match the original lap exactly.

State recording captures the vehicle transform and key dynamic values each tick. Playback reconstructs the visual path without re-simulating physics. This trades storage size for correctness -- a worthwhile tradeoff given the compression pipeline below.

Approach	Determinism Required	PhysX Compatible	Recommended
Input recording	Yes -- identical physics each playback	No -- PhysX non-deterministic	NO
State recording	No -- replays actual positions	Yes -- records what happened	YES

What We Do NOT Record

• Raw input axes (non-deterministic replay)
• Full PhysX solver state (massive, version-coupled)
• Other vehicles state (ghost is single-vehicle)
• Audio/VFX triggers (derived from playback state at runtime)

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Related Skills

Skill	When to Use
unity-camera-systems	Cinemachine setup, virtual camera configuration, camera blending
unity-save-load	Serialization patterns, persistent data, file I/O
unity-performance-optimization	Async patterns, memory management, compression

Topic Pages

• 2. GhostFrame Struct