Causality-0
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A deterministic replay engine for SCP:SL rounds
Rounds should remain replayable after they end
Overview
Causality-0 is a LabAPI-based replay plugin for SCP: Secret Laboratory.
It records server-side round state into a deterministic timeline, stores it as a .c0 binary replay, and reconstructs that round in-game with dummy actors, preserved timing, world-state restoration, and seed-aware playback rules.
Current stable release is V1.0.2.
The project is focused on reproducibility rather than cinematic approximation.
Whenever possible, playback restores recorded results directly instead of re-simulating fragile live runtime behavior.
Current capabilities
Deterministic timeline playback
Replay time is driven by frame index and per-file FPS metadata.
That keeps actor movement, interactions, projectiles, and optional voice packets aligned to the same timeline.
Actor lifecycle support
The replay pipeline now supports:
- players who join after recording started
- players who leave or disconnect before round end
- role changes during the round
- death lifecycle events
- delayed dummy spawning based on track start frame
- playback despawn on recorded leave
World-state persistence
The replay format now persists world state beyond actor tracks.
Current world reconstruction covers:
- map pickups present at recording start
- pickup create and remove events
- pickup movement persistence
- scorched-earth pickup cleanup before replay rebuild
- pure world pickup recreation from recorded type, position, rotation, and item properties
Projectile persistence
Projectile tracks are now written into .c0 files together with owner information.
Loaded replays can restore projectile playback without relying on the original live runtime state.
Deterministic door playback
Door replay now restores the recorded interaction result directly.
Loaded replays also use recorded spatial context to improve post-load door matching stability.
Replay compression
Replay files can now be saved as raw or Lzma-compressed payloads.
Loading auto-detects both formats.
Optional voice recording
Voice packet capture is available but configurable.
Voice playback still works for replays that already contain saved audio data.
Seed-aware replay loading
Replay files embed the recording map seed.
If the loaded replay seed does not match the current round seed, the plugin can force a restart so the replay can be loaded on the correct map seed next round.
.c0 protocol
Current replay protocol version is V16.
It currently stores:
| Field |
Notes |
| Map seed |
Used to validate world correctness |
| Replay FPS |
Saved in the file and restored on load |
| Actor tracks |
Position, view rotation, movement state, held item, stats |
| Audio packets |
Optional raw voice payloads with timestamps |
| Interaction frames |
Door timing, result, and recorded spatial context |
| Lifecycle events |
Role changes, death, leave/disconnect |
| World pickups |
Initial world pickup snapshot with absolute transform and item state |
| Pickup ops |
Add, move, remove |
| Projectile tracks |
Projectile frames and owner id |
Replay save containers currently support raw and Lzma envelopes, and load auto-detects them.
What is currently recorded
- player position and view rotation
- movement state and grounded state
- held item and firearm attachment code
- shooting and reload intent
- usable item start and cancel intent
- HP and AHP-like values
- optional raw voice packets
- door interaction timing, result, and recorded door position context
- late join and leave lifecycle changes
- projectile tracks and owner ids
- world pickups, pickup creation and removal, and pickup movement
- role changes and death lifecycle events
Command surface
c0 is available as a short alias of causality.
causality start
causality stop
causality save <name>
causality load <name>
causality spawn
causality play
c0 start
c0 stop
c0 save <name>
c0 load <name>
c0 spawn
c0 play
Behavior notes
start begins a new recording from the current statesave writes the current replay into CausalityRecords/<name>.c0load reads seed and FPS metadata before playbackload rebuilds world state when the replay seed matches the current round- if the replay seed does not match the current round, the plugin schedules a restart with the replay seed
play starts deterministic playback of the loaded or recorded timelinespawn can still be used for manual dummy spawning workflows
Configuration
The plugin now supports configuration through config.yml in the LabAPI plugin config directory.
Current config entries:
default_record_fps: 60
record_voice: false
replay_compression: Lzma
replay_compression_preset: Normal
Current config behavior
Core files
Current limitations
The project now has a formal V1.0.2 release, but some systems are still expanding.
Current known gaps or ongoing work include:
- ragdoll / corpse / death-scene ecosystem persistence
- automatic round recording policy and autosave workflow
- broader interaction replay coverage beyond the current implemented set
- dedicated replay inspection and debugging tools
Roadmap
Star History
License
This project is distributed under the terms of GNU AGPL v3.
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