Open-source drop-in replacement for the Miles Sound System (MSS) DLL

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OpenMiles is a clean-room reimplementation of the Miles Sound System (MSS) 6.6 API in Zig, designed as a drop-in mss32.dll replacement for legacy Windows games running on modern systems and under Wine.

It replaces the proprietary MSS audio stack with miniaudio for audio output, TinySoundFont for MIDI synthesis, and native decoders for MP3, OGG, and WAV (replacing MSS's proprietary ASI plugins), plus FLAC as a bonus format not in the original MSS.

Features

• Drop-in binary compatible -- exports the same stdcall ABI as mss32.dll
• Digital audio -- sample playback, streaming, volume/pan/pitch/loop control
• MIDI/XMIDI -- real-time synthesis via SF2 soundfonts, tempo control, beat callbacks, XMIDI loop/branch support
• 3D positional audio -- full spatial audio with distance attenuation, Doppler, cones, obstruction/occlusion
• ASI codec system -- built-in MP3/OGG/WAV/FLAC decoding; also loads external .asi plugins as fallback
• RIB provider system -- full provider enumeration and interface registration
• Filter API -- real-time low-pass filtering via miniaudio DSP nodes
• Reverb -- per-sample delay-based reverb
• Timer API -- background timer threads with configurable frequency
• Quick API -- high-level one-call playback
• Perceptual volume curve -- cubic attenuation matching the original MSS ~60dB dynamic range

Building

Requires Zig 0.15.2.

# Native build (Linux/Windows -- for tests)
zig build
zig build test

# Cross-compile for Windows (game deployment)
zig build -Dtarget=x86-windows -Doptimize=ReleaseSmall

Note: Native builds on macOS aarch64 (Apple Silicon) are not supported because Zig's stage2 backend does not implement the aarch64_aapcs_win calling convention used by the stdcall exports. Use Linux or Windows for native builds, or cross-compile to x86-windows.

The output DLL is at zig-out/bin/mss32.dll.

Usage

1. Build the Windows DLL with zig build -Dtarget=x86-windows -Doptimize=ReleaseSmall
2. Back up the original mss32.dll / MSS32.DLL in your game directory
3. Copy zig-out/bin/mss32.dll to the game directory (as both mss32.dll and MSS32.DLL on case-sensitive filesystems)
4. Run the game (natively on Windows, or via Wine on Linux/macOS)

Debug logging

Set OPENMILES_DEBUG=1 in your environment to enable verbose logging to openmiles.log in the game directory.

OPENMILES_DEBUG=1 wine YourGame.exe

Architecture

graph TD
    Game["Game (.exe)"] --> DLL["mss32.dll (OpenMiles)"]

    subgraph OpenMiles
        DLL --> API["src/api/<br/>C ABI exports (stdcall)"]
        DLL --> Engine["src/engine/<br/>Zig engine layer<br/>Sample, Sequence, DigitalDriver, Filter"]
        DLL --> RIB["src/rib/<br/>RIB provider system"]
        DLL --> Utils["src/utils/<br/>Logging, filesystem compat"]
        DLL --> Bindings["src/bindings/<br/>C implementations<br/>(AIL_debug_printf, AIL_sprintf)"]
    end

    Engine --> MA["miniaudio.h<br/>Audio output, decoding, mixing, 3D"]
    Engine --> TSF["tsf.h<br/>SoundFont (SF2) synthesis"]
    Engine --> TML["tml.h<br/>MIDI file parsing"]

    MA --> Backend["WASAPI / PulseAudio / CoreAudio"]

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API Coverage

367 functions exported, covering the full MSS 6.6 API surface (legacy waveOut/midiOut compatibility included; DIG_/MDI_ prefix aliases not yet exported). See docs/API_STATUS.md for the per-function implementation matrix.

Category	Status
Core System	Mostly implemented (some Windows/hardware-specific APIs are no-ops)
Digital Audio (Samples & Streams)	Fully implemented
MIDI / XMIDI	Core playback fully implemented; DLS utility and filter functions stubbed
3D Positional Audio	Fully implemented
RIB / ASI Plugin System	Fully implemented
Filter API	Low-pass filter implemented
Timer API	Fully implemented
Quick API	Fully implemented
Redbook (CD) API	Emulated (no audio -- games proceed gracefully)

Tested Games

Game	Status
Europa 1400: The Guild (Gold Edition)	Working -- MP3 streaming, WAV SFX, multiple drivers

Documentation

• API Implementation Status -- per-function status matrix
• API Support Matrix -- version compatibility overview
• Plugin & Codec Coverage -- ASI/M3D/FLT replacement status
• MSS Version History -- historical MSS releases

Dependencies

All dependencies are vendored single-header C libraries in deps/:

Library	Version	License	Purpose
miniaudio	v0.11.25	MIT-0 / Public Domain	Audio output, decoding, mixing, 3D
TinySoundFont	v0.9	MIT	SF2 synthesis
TinyMidiLoader	v0.7	Zlib	MIDI parsing

License

This project is licensed under the GNU General Public License v3.0.

OpenMiles is a clean-room reimplementation. It does not contain any code from the original Miles Sound System by RAD Game Tools.