205 lines
13 KiB
Markdown
205 lines
13 KiB
Markdown
# Architecture
|
||
|
||
> Companion to `CLAUDE.md` (product spec & tooling rules) and `Decisions.md` (why things
|
||
> are the way they are). This file describes **how the system is structured**. Update it
|
||
> whenever the structure changes.
|
||
|
||
## 1. System overview
|
||
|
||
Browser-first speech-to-text app. Whisper inference runs **in the browser by default**
|
||
via [Transformers.js](https://github.com/huggingface/transformers)
|
||
(`@huggingface/transformers`); no audio ever leaves the device for anonymous users.
|
||
Logged-in users may optionally route inference to the server.
|
||
|
||
```
|
||
┌──────────────────────────── Browser ────────────────────────────┐
|
||
│ │
|
||
│ React UI (App shell) │
|
||
│ ├─ ModelPicker (tiny → large, .en, quantized variants) │
|
||
│ ├─ FileDropzone (audio/video upload) │
|
||
│ ├─ LiveControls (microphone start/stop — D-016) │
|
||
│ ├─ TranscriptView (streaming partial results) │
|
||
│ └─ EngineToggle (device / server — logged-in only) │
|
||
│ │ postMessage protocol │
|
||
│ ▼ │
|
||
│ Inference Web Worker │
|
||
│ ├─ Transformers.js ASR pipeline (Whisper) │
|
||
│ ├─ Device selection: WebNN → WebGPU → WASM fallback │
|
||
│ └─ Model weights cached via browser Cache API │
|
||
│ │
|
||
│ Service Worker (PWA) │
|
||
│ ├─ Precached app shell (offline-first) │
|
||
│ └─ Works with zero network once installed + model cached │
|
||
└──────────────────┬───────────────────────────────────────────────┘
|
||
│ HTTPS (only when online / server engine chosen)
|
||
▼
|
||
┌──────────────────────────── Bun server ─────────────────────────┐
|
||
│ Bun.serve() — routes + HTML imports (no vite, no express) │
|
||
│ ├─ / → src/index.html (bundled React app) │
|
||
│ ├─ /inference.worker.js → worker bundle (Bun.build at startup, │
|
||
│ │ since Bun doesn't bundle `new Worker` graphs) │
|
||
│ ├─ /api/auth/* → Passport.js (local strategy) + sessions │
|
||
│ ├─ /api/transcribe → server engine (auth required) │
|
||
│ └─ /manifest.webmanifest, /sw.js → PWA assets │
|
||
│ bun:sqlite → users, sessions │
|
||
│ Server inference: faster-whisper (CTranslate2) Python sidecar, │
|
||
│ spawned & supervised by Bun (D-013) │
|
||
└──────────────────────────────────────────────────────────────────┘
|
||
```
|
||
|
||
## 2. Runtime & tooling
|
||
|
||
- **Runtime / bundler / test runner:** Bun only (`bun --hot src/index.ts` for dev,
|
||
`bun build src/index.html` for production, `bun test`). No vite/webpack/jest.
|
||
- **Frontend:** React 19, mounted from `src/index.html` via Bun HTML imports.
|
||
- **Server:** `Bun.serve()` with the `routes` option. No express.
|
||
- **DB:** `bun:sqlite`. No ORM planned initially.
|
||
|
||
## 3. Directory layout (target)
|
||
|
||
```
|
||
src/
|
||
index.ts # Bun.serve entry — routes, static, API
|
||
index.html # HTML entry, imports frontend.tsx
|
||
frontend.tsx # React root
|
||
App.tsx # top-level UI composition
|
||
components/ # ModelPicker, TranscriptionOptions, FileDropzone, LiveControls, TranscriptView, EngineToggle, AuthForms
|
||
lib/
|
||
audio.ts # decode + resample to 16 kHz mono Float32Array (Web Audio API)
|
||
live.ts # live-mode segment loop: RMS gate, LiveSegmenter, LiveTranscriber (pure, D-016)
|
||
mic.ts # microphone capture: AudioWorklet chunker (Blob URL) + fallback (D-016)
|
||
models.ts # model catalog: ids, sizes, dtype defaults per device, languages
|
||
modelCache.ts # "downloaded?" per model via Cache Storage (D-005; reused by M3 offline indicator)
|
||
engine.ts # engine abstraction: BrowserEngine | ServerEngine
|
||
worker/
|
||
inference.worker.ts # Transformers.js pipeline, WebNN/WebGPU/WASM selection
|
||
protocol.ts # typed postMessage messages (shared with UI)
|
||
pwa/
|
||
sw.ts # service worker (app-shell precache, /ort runtime cache)
|
||
precache.ts # placeholder-injection helpers shared by build + dev serve
|
||
register.ts # SW registration + update-toast flow
|
||
manifest.webmanifest
|
||
icons/ # generated by scripts/generate-icons.ts (not checked in)
|
||
server/
|
||
auth.ts # Passport.js wiring + session middleware adapter
|
||
db.ts # bun:sqlite schema + queries
|
||
transcribe.ts # server-side ASR endpoint (bridges the sidecar, M5)
|
||
server-py/ # faster-whisper sidecar (Python, D-013; M5)
|
||
tests/ # bun test
|
||
```
|
||
|
||
(Current state: M0–M3 built — browser transcription with the curated model
|
||
catalog, WebNN→WebGPU→WASM auto-selection (D-017), model switching,
|
||
language/task options,
|
||
and the installable offline PWA (`pwa/`, `scripts/build.ts` production build,
|
||
`dist/` serving in `src/index.ts`; browser-level offline behavior pending the
|
||
manual run in `tests/offline.md`). M4 accounts are built (`server/db.ts`,
|
||
`server/auth.ts`, `/api/auth/*`, `AuthForms`). M7 live microphone
|
||
transcription is built (`lib/live.ts`, `lib/mic.ts`, `LiveControls`, D-016;
|
||
in-browser run pending per `tests/live.md`). M5's server side is built —
|
||
`server-py/sidecar.py`, `server/transcribe.ts` (supervisor +
|
||
`/api/transcribe` + `/status`), `lib/engine.ts` (both engines, D-010), and
|
||
the catalog mapping in `lib/models.ts` — with graceful degradation when
|
||
Python/faster-whisper is absent; the `EngineToggle` component and App wiring
|
||
are the remaining M5 work; see `WorkBreakdown.md`.)
|
||
|
||
## 4. Key flows
|
||
|
||
### 4.1 Browser transcription (anonymous, default)
|
||
1. User picks a model in `ModelPicker` (curated catalog from `lib/models.ts`, with
|
||
size estimates and a Cache-API-backed "downloaded" badge). Selection alone
|
||
downloads nothing (D-020): the UI posts `{type:"load", modelId, device}` when a
|
||
browser-engine transcription starts (file drop / live start) or when the user
|
||
clicks the explicit **Download** button on the selected model; server-engine
|
||
runs never post a load. `device` is a preference
|
||
(`"auto" | "webnn" | "webgpu" | "wasm"`, default `"auto"`). An explicit `dtype`
|
||
override is expressible in the message but normally omitted.
|
||
2. Worker resolves the device (D-004, D-017): for `"auto"` it probes
|
||
`navigator.ml` (WebNN) first, then `navigator.gpu?.requestAdapter()` (WebGPU),
|
||
and picks in priority order WebNN → WebGPU → WASM; if pipeline creation on the
|
||
picked device throws, it retries down the same chain (WASM always last). An
|
||
explicit `"webnn"`/`"webgpu"` preference falls back straight to WASM. It then
|
||
resolves the catalog's dtype default for the device actually used and creates
|
||
the Transformers.js `automatic-speech-recognition` pipeline.
|
||
Download progress events are forwarded to the UI; the terminal
|
||
`{status:"ready", device}` message reports the backend actually selected, which
|
||
the UI surfaces. Loading a different model/device disposes the old pipeline
|
||
(`pipeline.dispose()`) before creating the new one.
|
||
3. Weights are fetched from the Hugging Face Hub **once**; Transformers.js stores them
|
||
in the browser Cache API, so subsequent loads (including offline) hit cache
|
||
(`lib/modelCache.ts` reads that cache for the downloaded badges).
|
||
4. User drops an audio/video file. Main thread decodes it with
|
||
`AudioContext.decodeAudioData`, downmixes to mono, resamples to 16 kHz,
|
||
transfers the `Float32Array` to the worker. For multilingual models the
|
||
`transcribe` message also carries `language` (or auto-detect) and `task`
|
||
(transcribe | translate).
|
||
5. Worker runs the pipeline (chunked, with timestamps), streaming partial results
|
||
back via `{type:"partial"}` messages; final result as `{type:"result"}`.
|
||
|
||
### 4.1b Live microphone transcription (anonymous, browser engine — D-016)
|
||
1. `LiveControls` starts a session: `getUserMedia` → `AudioContext` at the
|
||
device's native rate → AudioWorklet chunker (module from a Blob URL;
|
||
`ScriptProcessorNode` fallback) posts ~100 ms Float32 frames; the main
|
||
thread resamples each to 16 kHz (`lib/mic.ts`).
|
||
2. `LiveTranscriber` (`lib/live.ts`, pure) feeds frames through an RMS energy
|
||
gate: segments start at speech onset (short pre-roll), commit on trailing
|
||
silence or at ~25 s; pure silence is never transcribed.
|
||
3. The current segment is re-transcribed through the normal inference worker
|
||
on a rolling basis (throttled, single-flight, latest-snapshot-wins) as
|
||
*tentative* text; a committed segment gets one final pass and freezes.
|
||
`requestId` on the protocol messages correlates responses.
|
||
4. Stopping flushes the segmenter, drains pending final passes, and yields a
|
||
normal transcript (text + absolute-timestamped chunks) in `TranscriptView`.
|
||
Everything runs on-device; works offline like the file flow. Server-engine
|
||
live input is a recorded future want (WorkBreakdown M7, D-016).
|
||
|
||
### 4.2 Offline (PWA)
|
||
- Service worker (`pwa/sw.ts`, hand-rolled — D-007) precaches the built app shell
|
||
(hashed JS/CSS, `/`, worker bundle, manifest, icons) on install into
|
||
`whisper-shell-<version>`, cache-first thereafter; unknown navigations fall back
|
||
to the cached shell. `scripts/build.ts` injects the precache list + a
|
||
content-hash version into `dist/sw.js` via `pwa/precache.ts`; the dev server
|
||
injects an empty list ("dev"), making the dev shell network-first so HMR works.
|
||
- onnxruntime's `.wasm`/`.mjs` binaries are served from our origin at `/ort/*`
|
||
(never the jsdelivr CDN default) and runtime-cached cache-first into
|
||
`whisper-runtime-<version>` — they are required for offline inference but too
|
||
large to precache eagerly.
|
||
- Model weights live in the Cache API (`transformers-cache`) via Transformers.js —
|
||
independent of the SW, which never touches that cache (D-005). `/api/*` is
|
||
network-only.
|
||
- Updates: `pwa/register.ts` surfaces a waiting SW as a toast; accepting posts
|
||
`SKIP_WAITING`, activation drops old `whisper-*` caches, and the page reloads.
|
||
- Result: with the app installed and at least one model previously loaded, the full
|
||
transcription flow works with no network and with our server down (manual
|
||
verification procedure: `tests/offline.md`).
|
||
|
||
### 4.3 Server engine (logged-in only)
|
||
1. `EngineToggle` is visible only when a session exists.
|
||
2. `ServerEngine.transcribe()` uploads the decoded (or original) audio to
|
||
`POST /api/transcribe` with the chosen model id.
|
||
3. Server inference runs on **faster-whisper** (CTranslate2) in a Python sidecar
|
||
(`server-py/`) that Bun spawns and supervises (D-013; faster-whisper has no
|
||
browser/WASM build, so it is server-only — the browser stays on Transformers.js).
|
||
`src/server/transcribe.ts` bridges the sidecar's segment stream to the streamed
|
||
JSON-lines HTTP response (D-011). The shared catalog maps model ids to
|
||
`Systran/faster-whisper-*` CTranslate2 conversions. If the sidecar is absent,
|
||
the server engine reports unavailable; the browser/anonymous flow is unaffected.
|
||
4. Both engines implement the same `Engine` interface in `src/lib/engine.ts`, so the
|
||
UI is engine-agnostic.
|
||
|
||
### 4.4 Auth
|
||
- Passport.js **local strategy** behind a thin adapter that bridges Bun's
|
||
`Request`/`Response` to Passport's connect-style API (see Decisions.md D-008).
|
||
- Sessions in SQLite; session id in an HttpOnly cookie.
|
||
- Anonymous users are never blocked from browser inference — auth only unlocks the
|
||
server engine.
|
||
|
||
## 5. Invariants
|
||
|
||
- **Privacy:** browser-engine audio and transcripts never touch the network.
|
||
- **Anonymous-first:** every feature except the server engine works logged out.
|
||
- **Offline-first:** app shell + previously-downloaded models must work offline.
|
||
- **One browser inference codebase:** Transformers.js in the browser; the server
|
||
engine runs faster-whisper (D-013). The model catalog stays shared across both.
|
||
- **Worker isolation:** inference never runs on the main thread.
|