File size: 7,735 Bytes

# ThreadCast — Android Production Zips

Distributed mirror for the Android app's neural TTS assets. The eight zips here are downloaded by the app at runtime — first install of a neural engine pulls only what's needed (~74 MB for one Piper voice + shared data, ~26 MB for the Plus bundle, or ~145 MB for the full Kokoro bundle), and the user can manage each model individually from inside the app.

> Sibling: **`../extension/`** holds the Chrome extension's neural models in raw HF format. Both subtrees share the same engine families (Piper VITS, KittenTTS-nano, Kokoro StyleTTS2) — only the on-disk packaging differs.

---

## Layout

```
mobile-android/
└── v1/
    ├── threadcast-piper-shared-v1.zip                    (~11 MB) — espeak phonemizer data, downloaded once
    ├── threadcast-piper-en_US-amy-medium-v1.zip          (~63 MB) — Amy voice
    ├── threadcast-piper-en_US-lessac-medium-v1.zip       (~63 MB) — Lessac voice
    ├── threadcast-piper-en_US-ryan-medium-v1.zip         (~63 MB) — Ryan voice
    ├── threadcast-piper-en_US-hfc_female-medium-v1.zip   (~63 MB) — HFC Female voice
    ├── threadcast-piper-en_US-hfc_male-medium-v1.zip     (~63 MB) — HFC Male voice
    ├── threadcast-kitten-nano-en-v1.zip                  (~26 MB) — KittenTTS nano v0.1 fp16 (all 8 voices; "Local AI Plus")
    └── threadcast-kokoro-int8-en-v1.zip                  (~145 MB) — Kokoro int8 v0.19 (all 11 voices; "Local AI Studio")
```

**Versioning:** the `v1/` segment is part of the URL the runtime requests. Bumping to `v2/` lets future format changes ship without breaking older app builds — old apps keep pulling `v1/`, new apps pull `v2/`.

---

## What's inside each zip

The native [`AssetInstaller`](https://github.com/Pixel-Labs/Reddit-Reader/blob/main/packages/mobile/modules/threadcast-neural/android/src/main/java/app/threadcast/neural/AssetInstaller.kt) extracts each zip directly under `filesDir/sherpa-piper/` (Piper) or `filesDir/sherpa-kokoro/` (Kokoro), so the zip's internal layout = the on-device layout. No re-rooting, no per-file rules.

### Piper — shared espeak data

```
threadcast-piper-shared-v1.zip
└── espeak-ng-data/
    ├── phontab
    ├── phonindex
    ├── phondata
    ├── intonations
    ├── lang/
    ├── voices/
    └── … (full espeak-ng tree)
```

Downloaded once on the user's first Piper voice install. Skipped on every subsequent voice install.

### Piper — one zip per voice

```
threadcast-piper-en_US-amy-medium-v1.zip
└── en_US-amy-medium/
    ├── en_US-amy-medium.onnx        (~63 MB)
    └── tokens.txt
```

Five zips total — one per voice. Users only download the voices they want; selecting Amy doesn't pull Ryan.

### Kitten (Local AI Plus) — single bundle, all voices

```
threadcast-kitten-nano-en-v1.zip
├── espeak-ng-data/                  (separate copy from Piper's / Kokoro's — different on-disk root)
│   └── …
├── model.fp16.onnx                  (~24 MB)
├── voices.bin                       (~30 KB — 8 speaker embeddings)
└── tokens.txt
```

One download serves all 8 Plus voices — same style-vector-lookup pattern as Kokoro. The 8 speakers are baked into `voices.bin` in the order documented in `packages/mobile/modules/threadcast-neural/index.ts::KITTEN_VOICES`. **Never write the upstream engine codename in user-facing surfaces** — the Android UI labels this engine as "Local AI Plus" everywhere.

### Kokoro (Local AI Studio) — single bundle, all voices

```
threadcast-kokoro-int8-en-v1.zip
├── espeak-ng-data/                  (separate copy from Piper's — different on-disk root)
│   └── …
├── model.int8.onnx                  (~135 MB)
├── voices.bin                       (~5.7 MB — concatenated speaker embeddings, all 11)
└── tokens.txt
```

One download serves every Kokoro voice — switching speakers is a free style-vector lookup at synth time.

---

## How the runtime fetches these

**Mirror-and-fallback** — same pattern the extension uses for its `Pixel-Labs/threadcast-neural-models/{hf-cpu-mirror,hf-gpu-mirror}/` paths (see [`extension/src/offscreen/mirror-fetch.ts`](https://github.com/Pixel-Labs/Reddit-Reader/blob/main/packages/extension/src/offscreen/mirror-fetch.ts)). Each download is an ordered list of URLs; the installer tries each on failure and only surfaces an error if every URL is unreachable.

```
urls[0] = PRIMARY_BASE   = https://huggingface.co/Pixel-Labs/threadcast-neural-models/resolve/main/mobile-android/v1
urls[1] = FALLBACK_BASE  = (configurable — sibling HF repo, GitHub Release, private CDN, …)
```

Both bases need to serve the **same filenames** (the eight listed above). The fallback host is configured at app build time:

| Env var (set at build time) | Default | Purpose |
|---|---|---|
| `EXPO_PUBLIC_NEURAL_ASSETS_BASE_URL`     | `https://huggingface.co/Pixel-Labs/threadcast-neural-models/resolve/main/mobile-android/v1` | Primary mirror |
| `EXPO_PUBLIC_NEURAL_ASSETS_FALLBACK_URL` | unset | Optional fallback (omit for primary-only) |

The native installer:
- Tries `urls[0]` first. On HTTP 4xx/5xx or transport error, logs a warning and tries `urls[1]`.
- Only the LAST URL's failure surfaces to the UI as a download error — transient mirror outages are silent.
- Cancellation aborts immediately at any URL boundary.
- Verifies post-extract that every required file exists with non-zero size; rejects malformed zips even if the HTTP layer succeeded.

---

## Publishing workflow

1. **Produce the zips** from the local sherpa-onnx staging tree:

   ```sh
   pnpm --filter mobile produce:neural-zips
   ```

   Writes to `packages/mobile/dist/neural-assets/`. The script reads the locally-staged sherpa-onnx upstream artifacts (Piper voice ONNX files + KittenTTS-nano v0.1 fp16 bundle + Kokoro int8 v0.19 bundle + shared espeak-ng-data) and emits the eight zips with the correct internal layouts.

2. **Upload to Hugging Face** — the user-facing primary mirror lives at:

   <https://huggingface.co/Pixel-Labs/threadcast-neural-models/tree/main/mobile-android/v1>

   Drop all eight zips into that tree. HF preserves filenames as-is. No build steps, no metadata munging — they're just static assets behind a CDN.

3. **(Optional) Mirror to a fallback host.** Same eight filenames at any HTTPS endpoint. Common picks:
   - Sibling HF repo (`Pixel-Labs/threadcast-neural-models-mirror/v1/...`)
   - GitHub Release with `gh release upload v1 dist/neural-assets/*.zip`
   - Private CDN (R2, S3, etc.)

   Then ship the next app build with `EXPO_PUBLIC_NEURAL_ASSETS_FALLBACK_URL` set to the mirror's base URL.

---

## Per-engine download cost (user-facing)

| User intent | Files pulled | Network |
|---|---|---|
| Install **first** Local AI Lite voice (e.g. Amy) | `threadcast-piper-shared-v1.zip` + `threadcast-piper-en_US-amy-medium-v1.zip` | ~74 MB |
| Install **another** Local AI Lite voice (e.g. Lessac) | `threadcast-piper-en_US-lessac-medium-v1.zip` | ~63 MB |
| Install Local AI Plus | `threadcast-kitten-nano-en-v1.zip` | ~26 MB |
| Install Local AI Studio | `threadcast-kokoro-int8-en-v1.zip` | ~145 MB |
| Install every engine, all 5 Lite voices + Plus + Studio | every zip in `v1/` | ~496 MB |

The whole-bundle worst case is comparable to Spotify's "download an album for offline" workflow. Most users will pick one tier and stop there — Plus is the sweet spot at 26 MB for an 8-voice multi-speaker model.

---

## License

Per-project licenses retained from upstream — see the [parent README](../README.md#license) for the consolidated summary.