Action Replay System

Record player input as timestamped frames and replay it at any speed. Use it for ghost racing, replays, AI training data, QA reproduction, or highlight clips.

Structure

ActionRecorder (pure C# instance)
  - Adds InputFrame entries to ReplayData when input occurs

ActionPlayer (pure C# instance)
  - Plays ReplayData through Tick(deltaTime) and emits OnFrame events

InputFrame (struct)
  - Timestamp, ActionKey, Axis, IsPressed

ReplayData (class)
  - TotalDuration + List<InputFrame>

Quick Start

1. Record

using AchUtils.ActionReplay;

private readonly ActionRecorder recorder = new();

recorder.StartRecording();

public void OnJumpPressed()
{
    recorder.RecordButton("Jump", pressed: true);
    // Run real jump logic...
}

public void OnMove(Vector2 axis)
{
    recorder.RecordAxis("Move", axis);
}

ReplayData data = recorder.StopRecording();
SaveReplay(data);

2. Replay

private readonly ActionPlayer player = new();

void Update()
{
    player.Tick(Time.deltaTime);
}

void PlayGhost(ReplayData data)
{
    player.OnFrame += HandleFrame;
    player.Play(data, speed: 1f);
}

void HandleFrame(InputFrame frame)
{
    switch (frame.ActionKey)
    {
        case "Jump":  ghost.Jump();           break;
        case "Move":  ghost.Move(frame.Axis); break;
        case "Attack": ghost.Attack();        break;
    }
}

player.OnCompleted += () =>
{
    Debug.Log("Replay completed");
    player.OnFrame -= HandleFrame;
};

API

ActionRecorder

bool        IsRecording
ReplayData  LastRecording

void        StartRecording()
ReplayData  StopRecording()

void RecordButton(string key, bool pressed)
void RecordAxis(string key, Vector2 axis)
void Record(string key, Vector2 axis = default, bool pressed = true)

ActionPlayer

bool IsPlaying

void Play(ReplayData data, float speed = 1f)
void Stop()
void Tick(float deltaTime)

event Action<InputFrame> OnFrame
event Action             OnCompleted
event Action             OnStopped

InputFrame

float   Timestamp
string  ActionKey
Vector2 Axis
bool    IsPressed

Playback Speed

player.Play(data, speed: 0.5f);  // Slow motion
player.Play(data, speed: 2.0f);  // Double speed

Serialization

ReplayData is [Serializable], so it can be saved as JSON.

string json = JsonUtility.ToJson(data);
File.WriteAllText("replay.json", json);

string json = File.ReadAllText("replay.json");
ReplayData data = JsonUtility.FromJson<ReplayData>(json);

Use Cases

Use case	Description
Ghost racing	Replay a best run as a translucent object
Replay system	Watch the moments before death
AI training data	Use human input for imitation learning
Bug reproduction	Reproduce QA input exactly
Video clips	Auto-cut highlight moments

::: warning Networking Multiplayer replay sync requires a deterministic game loop. Physics-heavy games should drive physics manually, for example with Physics.simulationMode = Script. :::