MusicXML to MIDI converter

A suite of tools to convert MusicXML scores to MIDI via Musical MIDI Accompaniment (MMA).

Installation

• Install xmllint (included in libxml2 on most platforms)
• Install jq (only needed for automated tests)
• git submodule update --init --recursive
• npm install && npm run build

Converting a MusicXML score

• npm run --silent convert:unroll song.musicxml to unroll a MusicXML score by expanding all jumps and repeats at stdout
• npm run --silent convert:mma song.musicxml to both unroll a score and convert it to an MMA script at stdout
• npm run convert:midi /path/to/song.mma to convert an MMA script to MIDI /path/to/song.mid
• npm run --silent convert:timemap song.musicxml to convert a score to a timemap JSON file at stdout
• ./scripts/midi-timemap.js song.mid to convert a MIDI file to a timemap JSON file at stdout

Serving a conversion API endpoint

• PORT=3000 npm run develop for development (including hot-reload)
• PORT=3000 npm run start for production
• curl -sSf -F "musicXml=@test/data/salma-ya-salama.musicxml" -F "globalGroove=Maqsum" http://localhost:3000/convert -o "salma-ya-salama.mid"

Theory of operation

This converter aims to create a valid MMA accompaniment script out of a MusicXML score. The MMA script is then converted to MIDI using the bundled mma tool. To accomplish this, the converter expects to find the following information in the sheet:

• Chord information, expressed as harmony elements. MMA recognizes a large number of chords, but MusicXML's harmony representation is more general and can lead to invalid chord names. Refer to chords.musicxml for a reference on how to express all MMA-supported chords.

• Melody information, expressed as note elements. This is converted to an MMA SOLO sequence for each measure.

• Optional playback style information, expressed as sound/play/other-play elements with attribute @type = 'groove'. The content of this element represents the "groove" that is passed to MMA to generate an accompaniment. In case no such playback style information is found, or the specified style is not mapped to an existing MMA groove, the chords are played back as per the lead sheet without further accompaniment. Note that several styles can be specified in a single sheet, since the sound element is associated with measure or measure/direction elements. The groove can be overridden with the argument globalGroove.

Output metadata in the MIDI file

The produced MMA script / MIDI file contains metadata that can be useful to downstream consumers. This metadata is generally expressed as MIDI Marker meta messages, with the following syntax:

• Measure:N informs the consumer that the MIDI playback has reached measure N (0-based) in the score.
• Groove:X informs the consumer that the MIDI playback is henceforth using the specified playback style.