All subsystems
Platform

System overview

One compositor draws the preview and the export, so the two cannot drift.

Takes in

  • A screen, window, or region selection
  • Microphone and system audio
  • An optional camera

Gives out

  • A .recast project bundle
  • An exported .mp4 or .gif

Start reading at

  • lib.rs
  • Editor.svelte
  • +layout.svelte

Invariants

  • One compositor (RenderCore) serves preview and export, so a visual bug is fixed once.
  • @recast/editor never imports @tauri-apps; the desktop host injects every native capability.
  • The @recast/* packages ship source, so each app compiles their .svelte and .ts itself.

Recast is an offline-first desktop screen recorder + video editor. Stack: Tauri v2 (Rust backend) + Svelte 5 (runes) frontend, in a pnpm monorepo. The editor engine lives in the @recast/editor package; the desktop app (recast-desktop) is a thin host that wires it to native capabilities through injected services and host-hooks.

The guiding architectural bet: one compositor (RenderCore, WebGL2) drives both the live preview and the export, so the two can never diverge. FFmpeg is demoted from a second compositor to a pure muxer. Recording is Rust; editing/preview/export compositing is browser (WebView2 + WebGL2 + WebCodecs); persistence and heavy native work cross the Tauri IPC boundary.

Package & host map

graph TD
    desktop["recast-desktop<br/>(Tauri host app)"] -->|imports components| editor["@recast/editor<br/>(editor engine)"]
    desktop <-->|Tauri IPC| rust["Rust core (src-tauri)"]
    desktop -. "setEditorServicesForApp()<br/>setEditorHostHooks()" .-> editor
    editor --> media["@recast/media<br/>(decode + workers)"]
    editor --> captions["@recast/captions"]
    editor --> render["@recast/render"]
    editor --> ui["@recast/ui"]
    editor --> player["@recast/player"]
    web["recast-web"] --> editor
    web --> player

The @recast/* packages ship source (their exports map points at ./src), so each consuming app compiles their .svelte/.ts itself. This is load-bearing for Vite config (see 04-media-decode-and-workers.md).

Runtime process model

flowchart LR
    subgraph WV["WebView2 (frontend, one per window)"]
        svelte["Svelte UI"]
        gl["WebGL2 / WebCodecs"]
        wk["Web Workers ×5<br/>(mediabunny, filmstrip,<br/>render, export, smoothing)"]
        svelte --> gl
        svelte --> wk
    end
    svelte <-->|"invoke() / ipc::Channel events"| core["Rust core"]
    core --> ff["FFmpeg sidecar"]
    core --> sqlite[("SQLite (export queue + index)")]
    core --> fs["filesystem (.recast, temp)"]

Conventions

  • path:line citations point at the real source at time of writing.
  • Diagrams are Mermaid, written inline in the markdown so the source of a diagram is readable without rendering it.
  • "Host" means the desktop app (apps/desktop); "package" or "engine" means @recast/editor.
  • Every page states its inputs, outputs, entrypoints, and invariants in frontmatter. Those are the summary; the prose is the detail.
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