oxideav-midi

Pure-Rust MIDI — Standard MIDI File (.mid / SMF) parser + transport metadata + soft-synth scaffold. Zero C dependencies, zero FFI, zero *-sys.

External instruments (SoundFont 2 .sf2, SFZ, DLS Level 1/2) are loaded from disk at runtime; nothing is bundled in the binary. A pure-tone oscillator fallback lets the synth produce some output even when no instrument bank is installed.

Part of the oxideav framework but usable standalone.

Status

• smf — full SMF (Type 0 / 1 / 2) parser. Header (MThd), tracks (MTrk), variable-length quantities (bounded to 4 bytes per spec), every channel-voice message, sysex (F0 / F7), and the common meta events (tempo, time signature, key signature, text, marker, end-of-track, SMPTE offset, sequencer-specific). Running status is honoured; chunk lengths are validated against remaining bytes; total events per file are capped at 1 M to keep malformed input bounded.
• paths — per-OS SoundFont/SFZ/DLS search paths plus the OXIDEAV_SOUNDFONT_PATH env-var override.
• instruments::sf2 — full SoundFont 2 RIFF reader and voice generator. Walks RIFF/sfbk → LIST INFO / LIST sdta (smpl + optional sm24) / LIST pdta (phdr / pbag / pgen / inst / ibag / igen / shdr); cross-resolves the preset → instrument → zone → sample chain. Honours the keyRange / velRange filters; the sampleID / instrument / sampleModes / *Tune / overridingRootKey generators; the volume DAHDSR envelope (gens 33-38) and initialAttenuation (gen 48); the modulation DAHDSR envelope (gens 25-30) routed into pitch (gen 7) and filter cutoff (gen 11); the initial low-pass biquad filter (gens 8/9); and the exclusive-class drum cut (gen 57). PCM storage is signed 24-bit (i32) — sm24 lower bytes are combined with smpl's 16-bit upper bytes when present, otherwise the 16-bit value is widened. Stereo zones (LEFT / RIGHT sample_type + cross-linked sample_link) render natively in stereo, bypassing the mixer's mono-pan law. Chunk lengths and array indices are bounds-checked against the loaded data; total samples capped at 256 Mi frames, total pdta records capped at 16 Mi, so malformed files cannot allocate beyond the spec ceiling.
• instruments::sfz — text patch reader plus voice generator. Tokenises SFZ syntax (line + block comments, headers, opcode name=value pairs with space-bearing values), walks <control> / <global> / <master> / <group> / <region> sections, flattens inheritance into one fully-resolved opcode map per region, and (via SfzInstrument::open) reads every referenced sample off disk against the SFZ file's directory + the active default_path. Strongly-typed fields: lokey / hikey / lovel / hivel, pitch_keycenter, key (sets all three), loop_start / loop_end / loop_mode, tune / transpose, volume, pan, trigger. Note names (C4, c#4, Db5) parse alongside decimal MIDI keys. Voice generation decodes the WAV sample bytes (8/16/24/32-bit PCM and IEEE_FLOAT) into mono f32, picks the matching region by (key, velocity), shifts pitch off pitch_keycenter + tune + transpose, applies a DAHDSR amplitude envelope from ampeg_* opcodes, and runs a vibrato LFO from lfo01_freq / lfo01_pitch / lfo01_delay. #include is rejected with Error::Unsupported; #define is preserved verbatim.
• instruments::dls — DLS Level 1 + 2 RIFF reader plus voice generator. Walks the RIFF/DLS form (colh / vers / ptbl / lins-list / wvpl-list / INFO-list), surfaces the parsed bank with instrument → region → wave-pool topology, wsmp loop / pitch / gain headers, wlnk cue-table references, and art1 / art2 articulation connection blocks (raw — connection enums not interpreted). Voice generation picks the matching instrument by MIDI program, picks a region by (key, velocity), resolves the wlnk → ptbl → wave-pool entry, decodes the PCM (8/16-bit WAV-shaped) into mono f32, shifts pitch off the wsmp.unity_note, and plays the sample through the shared sample-playback voice. Loop modes: forward loop (WLOOP_TYPE_FORWARD, DLS1) and release loop (WLOOP_TYPE_RELEASE, DLS2). art1/art2 connection-block evaluation is deferred — the parsed blocks remain on the bank for round-2 callers.
• instruments::tone — pure-tone fallback (sine / triangle / saw / square) so the synth produces something even with no on-disk bank.
• mixer — polyphonic voice pool (32 voices) with stereo mixdown, per-channel volume / pan / sustain pedal handling, oldest-voice preemption when the pool is full, channel/poly aftertouch routed to per-voice pressure, RPN 0 (pitch-bend range) handling, and exclusive-class drum cuts. Native stereo voices (SF2 stereo zones) are rendered through their own L/R buses, bypassing the mono-pan law.
• scheduler — round-3 SMF event scheduler. Merges every track into a single time-ordered stream, converts ticks → samples against the current tempo + division (samples_per_tick = us_per_quarter * sample_rate / (1_000_000 * ticks_per_quarter)), and dispatches every event into the mixer at the right audio sample.
• downloader — stub that names a planned default bank (TimGM6mb) but currently returns Error::Unsupported.

The decoder factory is registered under codec id "midi". Round-3 wires SMF events end-to-end: send_packet parses the SMF and primes the scheduler; receive_frame returns interleaved S16 stereo PCM (1024 samples per channel at 44 100 Hz) until both the event stream and the voice pool have run dry. Without an on-disk bank the registry-built decoder uses the pure-tone fallback; for SoundFont 2 playback build a MidiDecoder directly with an Sf2Instrument.

Coverage today (round 9): full SF2 voice with sm24 24-bit samples, stereo zones, DAHDSR volume + modulation envelopes, low-pass biquad filter (gens 8/9), modEnv→pitch / modEnv→filter routing (gens 7/11), exclusive-class drum cuts (gen 57), pitch bend with RPN 0 range, channel/poly aftertouch; SFZ voice generator with DAHDSR amplitude envelope (ampeg_*) and vibrato LFO (lfo01_freq / lfo01_pitch); DLS Level 1 + 2 voice generator (parser-driven region selection, wsmp loop info, unmodulated sample playback — articulation art1/ art2 block interpretation is round 2). All three instrument paths share one SamplePlayer voice for sample playback + DAHDSR + vibrato + pitch bend.