Henkan

Hello, I’ve continued working on Henkan, my osu!mania ↔ Etterna converter, and released several major updates since my first ship.

The biggest addition is full skin conversion. Henkan can now convert osu!mania skins into Etterna noteskins and convert Etterna noteskins back into osu!mania skins. This required handling lane textures, sprite sheets, high-resolution assets, Lua files, metrics, redirects, and the different ways both games structure their skins.

I also added customizable difficulty name presets. Exported charts can automatically use information such as the title, artist, creator, original difficulty name, or calculated MSD. Users can also change the column width when exporting to osu!mania.

Several conversion issues were fixed, including problems with extreme BPM values, export filenames, media files, and configuration support. The web version now behaves much more like the desktop app, with matching exports and features across Rust, Tauri, and WebAssembly.

I also improved the project outside of the main application. Windows builds now use NSIS installers, Henkan is available through the AUR, the documentation has been expanded, the CI workflows have been cleaned up, and I added an end-to-end test for the skin converter.

Keeping the desktop and web versions consistent is still one of the hardest parts of the project, since converter changes often need separate implementations for Rust and WebAssembly. My goal is still to make Henkan the most reliable way to move charts and skins between osu!mania and Etterna without losing important data.

Hello, I made an osu!mania ↔ Etterna converter called Henkan (変換).

I started the project because I noticed that most existing converters didn’t preserve maps correctly. Timing would drift, BPM changes would be lost or simplified, and long notes would often break during conversion. I wanted to build a converter that focused on accuracy instead of quick conversions.

Henkan converts beatmaps between osu!mania (.osu / .osz) and Etterna/StepMania (.sm) while preserving the original chart as closely as possible. It keeps millisecond-accurate note timing, supports multiple BPM changes, correctly converts long notes, preserves metadata such as title, artist, creator, difficulty, and preview point, and keeps background references.

The application is written as a native desktop app using Rust, Tauri, and React, making it lightweight and fast on Windows, macOS, and Linux. It also supports converting entire packs, allowing users to process many maps at once instead of converting them individually.

One limitation is that scroll velocity (SV) is not converted from osu!mania to StepMania because the .sm format does not have an equivalent representation for osu!’s green-line SV changes.

My goal with Henkan is to provide a reliable converter that players can trust to preserve their charts accurately instead of introducing timing errors or losing important map information.