Initial commit: Win Dictation - AI Voice to Text for Windows with automatic model selection

src/DESIGN.md

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+# Windows Dictation App Design Document
+
+## Goals
+- Create a "polished" Windows app for dictation.
+- Small memory footprint.
+- Real-time transcription.
+- Global hotkey support.
+- On-demand GPU usage.
+
+## Architecture
+
+The application is a native **Win32 C++** application. It avoids heavy UI frameworks (Electron, .NET, Qt) to strictly adhere to the "small memory footprint" requirement and integration with the C++ codebase.
+
+### Components
+
+1.  **Main Entry (`WinMain`)**:
+    - Initializes the application.
+    - Registers the global hotkey (`RegisterHotKey`).
+    - Creates the main window (hidden by default).
+    - Creates the System Tray icon (`Shell_NotifyIcon`).
+    - Runs the standard Windows Message Loop.
+
+2.  **UI Layer (Win32 API)**:
+    - **Main Window**: A simple Dialog or Window containing:
+        - `EDIT` control (Multiline, VScroll) for text output.
+        - `BUTTON` controls for Record/Stop/Clear.
+        - `STATUS` bar for model state.
+    - **Tray Icon**: Context menu for Open/Exit.
+
+3.  **Audio & Inference Layer (`Transcriber`)**:
+    - Runs in a separate **Worker Thread** to prevent freezing the UI.
+    - **Audio Capture**: Uses `SDL2` (reusing `common-sdl.cpp` logic) for cross-platform consistency with the repo, or potentially native WASAPI if dependencies become an issue. For now, SDL2 is assumed as it's standard in this repo.
+    - **Inference**: Uses `whisper.cpp` library (`whisper_full`).
+    - **VAD (Voice Activity Detection)**: Uses the simple energy-based VAD from `common.cpp` to detect when to transcribe.
+
+### Threading Model
+
+- **UI Thread**: Handles Windows messages, paints the UI, processes hotkeys.
+- **Worker Thread**:
+    - Loops continuously when "Recording" is active.
+    - Captures PCM audio chunks.
+    - Runs `whisper_full` on the buffer.
+    - Uses `PostMessage(hWindow, WM_USER_TEXT_READY, ...)` to send transcribed text back to the UI thread safely.
+
+### Resource Management (GPU/Memory)
+
+- **Startup**: Does *not* load the model immediately to save RAM/VRAM.
+- **On Record**: Checks if context exists. If not, loads the model (`whisper_init_from_file`).
+- **Inactive Timeout**: A timer in the UI thread monitors inactivity. If inactive for X minutes, it signals the worker to destroy the whisper context (`whisper_free`), releasing VRAM.
+
+### Key APIs
+- `RegisterHotKey`: For global shortcuts.
+- `Shell_NotifyIcon`: For system tray.
+- `CreateWindowEx` / `DialogBox`: For UI.
+- `whisper_full`: For inference.
+
+## File Structure
+
+- `main.cpp`: Entry point, Window Proc, Message Loop.
+- `transcriber.h/cpp`: Wraps the Whisper context and SDL audio loop.
+- `resource.rc`: Defines the UI layout (dialogs, menus, icons).
+- `CMakeLists.txt`: Build definition.
+
+## Future Improvements
+- Settings dialog to select Model path.
+- Select Audio Input device.
+
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