Witbound for Windows (and Linux) — desktop companion

Kotlin + Compose Desktop app that does the slow part of Witbound on a computer — transcribe + align an ebook with its audiobook — then sends the finished book to the phone over the LAN, already synced. Same pairId + RASM map + _witbound._tcp protocol as the Mac app, so the phone can't tell which computer sent it.

Code signing

Windows builds are signed through the SignPath Foundation's free code-signing program for open-source projects (certificate by SignPath.io). Signed installers ship once the project is approved.

Layout

• src/main/kotlin/app/witbound/core/ — reused verbatim from the Android app (Aligner, Tokenizer, SyncMapBuilder, EpubParser) + extracted models, SyncMap (RASM), SyncNet (pairId). Pure JVM; unit-tested (CoreTest).
• engine/ — Transcriber (drives a whisper.cpp binary; GPU comes from the binary's build) and SyncPipeline (hash → optional network → transcribe → align → RASM → optional upload).
• net/ — WitboundLink (wire types), LanServer (JDK HTTP file server: /pairs, /file/ with Range, /map/, POST /delivered), PhoneBrowser (jmDNS discovery), Lan (offer POST + local IPs).
• Model.kt / Main.kt — the app + Compose UI.

The GPU speed lever

Speed = which whisper.cpp binary you bundle. Build whisper.cpp with:

• CUDA for NVIDIA (fastest; the 100×-class path) — -DGGML_CUDA=ON
• Vulkan for any DX12 GPU (AMD/Intel/NVIDIA) — -DGGML_VULKAN=ON
• CPU fallback otherwise. The app just runs whisper-cli; it offloads to the GPU automatically. Pick the model for the speed/accuracy trade-off (base.en is a good default; small.en for better timings; a distil model for max speed).

Dev run (any OS with a whisper build + ffmpeg)

WITBOUND_WHISPER=/path/to/whisper-cli \
WITBOUND_FFMPEG=/path/to/ffmpeg \
WITBOUND_MODEL=/path/to/ggml-base.en.bin \
./gradlew run

Tests

./gradlew test            # core (RASM, pairId vector, align+build)
# real end-to-end (needs a whisper build):
WITBOUND_WHISPER=… WITBOUND_FFMPEG=… WITBOUND_MODEL=… \
WB_EPUB=… WB_AUDIO=… ./gradlew test --tests "*IntegrationTest*"