XMrs — SoundTracker file format library

A no_std-friendly Rust library to read, edit and serialize SoundTracker data — with pleasure.

Because "Representation is the Essence of Programming".

Supported formats

Historical module files — imported into xmrs's in-memory Module model:

The umbrella feature import enables all of them at once (and is on by default together with std).

The Module model

xmrs exposes one editor-friendly data model, regardless of what was loaded:

Module ─┬─ Instrument ─┬─ InstrDefault ─┬─ VoiceSetup     (envelopes, vibrato, filter, panning)
        │              │                ├─ InstrumentBehavior  (NNA, DCT, DCA)
        │              │                ├─ Keyboard       (per-input-note sample + transposition)
        │              │                ├─ InstrMidi
        │              │                └─ Sample         (loop & sustain-loop)
        │              ├─ InstrEkn       (Euclidean-rhythm instrument)
        │              ├─ InstrMidi      (MIDI instrument)
        │              ├─ InstrOpl       (Yamaha OPL)
        │              ├─ InstrSid       (MOS6581 SID voice)
        │              └─ InstrRobSid ── InstrSid  (Rob Hubbard-style)
        └─ Track ─ Vec<Cell> ──────┬─ CellEvent       (None, NoteOn{pitch,velocity}, NoteOnGhost{…}, InstrReset, NoteOff{retrig}, NoteCut, NoteFade)
                                   └─ Vec<TrackEffect>  (discrete / per-trigger effects only — see below)

The continuous-modulation families (Vibrato* / Tremolo* / Panbrello* / Portamento* / TonePortamento / VolumeSlide* / ChannelVolumeSlide* / PanningSlide*) and every song-level global (Bpm / Speed / GlobalVolume + slides) live on Module::automation: Vec<AutomationLane> instead, extracted upstream from TrackImportUnit at import time. The MidiMacro global effect relocates to Cell::effects as TrackEffect::MidiMacro during materialisation. Navigation globals (PatternBreak / PositionJump / PatternLoop / PatternDelay) are absorbed into TimelineMap at import time.

Tracks are arranged on the timeline by Clips; see The DAW timeline layer below for the full layout.

InstrDefault is split into three orthogonal sub-types so each concern lives in one place: [VoiceSetup] (how the voice sounds once triggered), [InstrumentBehavior] (what happens when the same instrument retriggers), [Keyboard] (per-input-note sample / pitch remap, used by IT drum kits).

Per-module playback semantics are bundled into a single [CompatibilityProfile] field on Module:

• format — source-format tag (Xm, S3m, It, Mod, Unknown). Informational only — no playback decision reads it.
• quirks — the orthogonal switches each historical tracker flips: FT2 pitch-slide overflow, S3M period clamp, arpeggio LUT, pattern-loop resume, tremor state, IT vibrato tick-zero, pan reset policy, and so on.

Named constructors materialise the canonical configurations: CompatibilityProfile::ft2(), it214(), it215(), st3(), pt(), modern() (the editor-friendly default — all quirks off). Importers pick the right constructor for the source file and overlay any header-driven flags on top.

Module also carries a [Vec<ChannelDefault>] for per-channel initial state (panning, channel volume, mute, surround). S3M's channel_settings and IT's initial_channel_pan / initial_channel_volume populate it; XM/MOD leave it empty.

The DAW timeline layer

The historical Pattern → Row → TrackUnit matrix is gone — Module stores songs natively in a DAW-style layout, populated by the importers (or on demand via [xmrs::daw::build_timeline::build_timeline_layer]):

Module ─┬─ tracks        : Vec<Track>            (one per song + instrument)
        ├─ clips         : SortedClips           (placements on the timeline)
        ├─ automation    : Vec<AutomationLane>   (lanes for every continuous modulation
        │                                         + Bpm / Speed / GlobalVolume song-levels,
        │                                         extracted at import or via the edit API)
        ├─ timeline_map  : TimelineMap           (linearised pattern_order)
        └─ song_loop_to  : Option<u32>           (XM/MOD restart byte, as an absolute tick)

• Track owns the actual Vec<Cell> for a given (song, instrument) pair. Two special instrument values are reserved: EFFECT_ONLY_INSTRUMENT for segments that carry only effects (no note/instrument), and the index of an InstrumentType::Euclidean(…) wrapper for collapsed Euclidean rhythm tracks.
• Clip places a Track onto a (song, target_channel) lane at a given position_tick, with end_tick stored at extract time so half-open active_at lookups are exact.
• SortedClips keeps clips sorted by (song, target_channel, position_tick) and exposes from_unsorted, lane, active_at, modify, insert.
• TimelineMap flattens the pattern_order into absolute ticks and absorbs every navigation effect (Bxx / Dxx / E6y / EEy
  • restart byte) at import time — the player navigates through timeline_map.entries linearly, no row-by-row jump interpretation.
• AutomationLane carries the modulation curves: Points for typed (tick, value) curves (Bpm/Speed/GlobalVolume), Lfo for Vibrato/Tremolo/Panbrello, Slide for VolumeSlide/Portamento/ ChannelVolumeSlide/PanningSlide/BpmSlide/GlobalVolumeSlide, Glide for TonePortamento.

The import pipeline (run by every import_* feature) is:

build_timeline_map        ── linearise order + absorb navigation
  → extract_tracks_and_clips     ── split by instrument, emit clips
  → dedupe_tracks_by_content     ── fuse bit-identical tracks
  → auto_convert_strict_euclidean_tracks    ── collapse Bjorklund tracks
  → extract_per_track_lanes_from_patterns   ── Vibrato/Tremolo/Panbrello/
                                              Portamento/TonePortamento/
                                              VolumeSlide/ChannelVolumeSlide/
                                              PanningSlide → AutomationLanes
  → extract_song_lanes_from_patterns        ── Bpm/Speed/GlobalVolume + slides

[Module::row_at(song, pattern, row)] is the single cell-resolution API. It looks up the absolute tick in timeline_map, picks the active clip on each (song, target_channel) lane via SortedClips::active_at, and returns one (Cell, Option<usize>) per channel (the Option<usize> is the active Track's instrument index). All reads go through the DAW layer; there is no legacy fallback. The [xmrs::edit] module exposes incremental commands (cmd_create_clip, cmd_duplicate_clip, …) for editor / DAW UIs, with apply/undo round-trip verified by a proptest suite.

Euclidean rhythm instruments

InstrEkn (InstrumentType::Euclidean) stores (events, steps, rotation, prototype): a single Cell prototype plus a Bjorklund pattern. When a strict single-note repetition is detected, auto_convert_strict_euclidean_tracks collapses the Track to one row and routes the cells through a canonical euclidean_pattern(events, steps) generator at playback time. Bit-identical to the original — but the on-disk track is one row instead of N.

Loading a file

use xmrs::prelude::*;

let bytes = std::fs::read("song.xm")?;

// Auto-detect: tries XM → S3M → IT → MOD.
let module = Module::load(&bytes)?;

// Or target a specific format:
let module = Module::load_xm(&bytes)?;

println!("{} — {} tracks, {} clips", module.name, module.tracks.len(), module.clips.len());

Format-specific constructors are also available: Module::load_mod, load_xm, load_s3m, load_it. SID is imported via its own entry point, xmrs::import::sid::sid_module::SidModule::load, and is not part of the auto-detect path.

Serialization

Module derives serde::Serialize / Deserialize, so you can round-trip it through any serde codec.

Examples

Run from the xmrs crate directory:

# Dump any supported module file:
cargo run --features=demo --example xmrs -- -f path/to/song.xm

# Dump an XI (Fast Tracker II instrument) file:
cargo run --example xmi

# Exercise the bundled SID parsers (Rob Hubbard tunes):
cargo run --example sid

Cargo features

Defaults: ["std", "import"].

no_std builds

The crate compiles fully no_std with no math backend at all. Every former f32 site on the runtime path has been folded to integer Q-format arithmetic — pitch / period / frequency tables, the LFO (waveform.rs), the IT importer's c5_speed_to_finetune (binary search via linear_frequency_to_period), envelopes, panning, filter, sample interpolation. No libm, no micromath, no num-traits.

Importer features parse fixed-layout tracker headers through a cursor-based helper ([xmrs::import::bin_reader]) — no third-party binary-parsing crate is involved. serde is the only direct runtime dependency (the IT keyboard's [Option<_>; 120] arrays ride on an inline serde_with shim — no serde-big-array).

# Minimal build, no importers (pre-baked blobs only):
cargo build --no-default-features --release

# Embedded build, MOD + XM importers only:
cargo build --no-default-features --features "import_mod import_xm" --release

Concert pitch (440 Hz / MIDI-aligned)

Notes resolve to MIDI-aligned frequencies by default: A-4 plays at exactly 440 Hz, C-4 at 261.626 Hz, etc. This means tracker output mixes cleanly with any 440-Hz-aligned source (MIDI sequencers, DAW samples, commercial audio) without a detune.

Two reference constants govern this, both in crate::fixed::tables:

The legacy values are exposed for bit-numerical comparison against reference players (OpenMPT, libxmp, schism, ft2-clone). Most users should leave the defaults alone — that's what makes a tracker note sound in tune against modern audio.

Embedded / footprint-sensitive builds

If you're targeting tight flash budgets, don't ship the importers. Parse modules on a host machine, serialise the resulting Module through any serde codec (Module derives Serialize / Deserialize), and load the resulting blob on-device. postcard is a good no_std default — it's alloc-only by default, varint-encoded, and produces compact output; pair it with flate2 or miniz_oxide if you need further compression. You end up with a much smaller binary that still manipulates the full Module model.

License

MIT © Sébastien Béchet. See LICENSE.