midi-file-mcp

Parses binary MIDI files into structured event objects (note-on, note-off, control change, tempo, time signature) by reading variable-length quantities and status bytes according to the MIDI 1.0 specification. Leverages Tone.js's MIDI parsing infrastructure to handle multiple tracks, timing divisions, and meta-events while preserving absolute and relative timing information for downstream manipulation.

Extracts and filters MIDI events by track index, channel, event type (note-on/off, CC, program change), or time range using in-memory array operations on the parsed event structure. Allows selective manipulation of multi-track MIDI files by creating new track subsets without modifying the original file, preserving timing relationships and metadata.

Constructs new MIDI events (note-on, note-off, control change, tempo, time signature) with specified parameters (pitch, velocity, duration, channel, timestamp) and inserts them into existing track structures at precise timing positions. Handles automatic delta-time recalculation when inserting events to maintain proper MIDI timing relationships and prevents timing conflicts through validation.

Converts in-memory MIDI event structures back into binary MIDI file format (.mid) by encoding events as status bytes, variable-length quantities, and delta-time values according to MIDI 1.0 specification. Handles track chunking, header generation with timing division metadata, and file I/O to produce valid, playable MIDI files that can be opened in any DAW or MIDI player.

Exposes MIDI parsing, filtering, creation, and export capabilities as MCP tools that can be called by LLM agents and other MCP clients through standardized request/response protocol. Handles tool schema definition, parameter validation, error handling, and result serialization to enable natural language composition of MIDI workflows (e.g., 'extract the melody from this MIDI file and transpose it up a fifth').

Identifies and extracts tempo (BPM) and time signature meta-events from MIDI files, exposing them as structured data with absolute timestamps. Supports insertion of new tempo/time signature changes at arbitrary positions, enabling tempo mapping, time signature analysis, and rhythmic transformation of MIDI compositions while preserving musical structure.

Applies transformations to note pitch (transposition, octave shifting, scale quantization) and velocity (scaling, randomization, humanization) across MIDI events using mathematical operations on note data. Supports batch transformations across entire tracks or filtered subsets, enabling algorithmic music generation, humanization, and harmonic manipulation without manual event iteration.