MIDI Class

MIDI Class

This is the module responsible for parsing MIDI files into objects readable by Sequencer class.

Tip

If you encounter any errors in this documentation, please open an issue!

Table of Contents

• MIDI Class
  • Table of Contents
  • Importing
  • Initialization
  • Properties
    • tracksAmount
    • timeDivision
    • midiName
    • rawMidiName
    • copyright
    • tempoChanges
    • loop
    • format
    • firstNoteOn
    • duration
    • midiPorts
    • midiPortChannelOffsets
    • usedChannelsOnTrack
    • keyRange
    • lyrics
    • RMID Related
      • embeddedSoundFont
      • bankOffset
      • RMIDInfo
    • tracks
  • Functions
    • MIDIticksTosecond
    • writeMIDIFile
  • How the file is stored
    • Extracting info from midi.tracks

Importing

// normal install
import {MIDI} from "./spessasynth_lib/midi_parser/midi_loader.js";
// npm package
import {MIDI} from "spessasynth_lib";

Tip

Using the npm package? Make sure you've read this

Initialization

const parsedMIDI = new MIDI(arrayBuffer);

• arrayBuffer - an arrayBuffer anstance of the midi file.

Properties

tracksAmount

The amount of tracks in the file.

console.log(`this file has ${parsedMIDI.tracksAmount}`);

timeDivision

The time division of the midi file. Used by the Sequencer class

console.log(`this sequence's time division is ${parsedMIDI.timeDivision}`);

midiName

The sequence's name. The first track's Track Name's event text.

console.log(`This sequence is named "${parsedMIDI.midiName}"`);

Tip

This property uses basic decoding. If the name is encoded in a different encoding, like shift_jis, it might be better to use rawMidiName.

rawMidiName

The sequence's name, as a raw Uint8Array. Useful for handling unusual encodings.

console.log(new TextDecoder("shift-jis").decode(parsedMIDI.rawMidiName)); // ダメなりんご！！

copyright

The decoded copyright and description of the file. Also includes the Sound Canvas display messages.

console.log(`Midi file description: ${parsedMIDI.copyright}`);

tempoChanges

Ordered from last to first, all the tempo changes in the file. Will always contain at least 1 tempo (the default 120BPM).

[
   {
       tempo: 140 /* tempo in BPM */,
       ticks: 5437 /* absolute amount of MIDI Ticks from the start */
   },

   /*...*/

   {
       tempo: 120,
       ticks: 0
   }
];

loop

The points of the loop detected in the MIDI file in ticks. If there's nothing detected, the loop will start from the first note on event and end will be the last note off. Current looping detection is: CC 2/4, 116/117 and "start", "loopStart" and "loopEnd" markers.

console.log(parsedMIDI.loop); // {start: 1294, end: 49573}

format

The MIDI file format. Usually 0 or 1, rarely 2.

console.log(parsedMIDI.format); // 1

firstNoteOn

The tick number of the first noteOn event in the sequence. Can be used to skip the initial silence.

console.log(parsedMIDI.firstNoteOn); // 1294

duration

The sequence's duration in seconds.

console.log(parsedMIDI.duration); // 125.64;

midiPorts

The detected midi ports for each track. Each port represents a batch of 16 channels.

console.log(parsedMIDI.midiPorts); // [0, 0, 0, 1, 1, 2, ...]

midiPortChannelOffsets

The channel offsets for each MIDI port, using the SpessaSynth method

console.log(parsedMIDI.midiPortChannelOffsets); // [16, 0, 48, 32, ...]

usedChannelsOnTrack

All the channels that each track refers to. An array of Sets.

console.log(parsedMIDI.usedChannelsOnTrack) // [ Set[0, 1, 2, 3, 4] ] - this sequence has 1 track which plays on channels 0, 1, 2, 3 and 4

keyRange

The key range of the sequence. The lowest pressed key and highest.

console.log(parsedMIDI.keyRange); // {min: 0, max: 127}

lyrics

The detected lyrics, stored as binary text data, as MIDIs can use different encodings. Stored as an array of Uint8Arrays, each is a single lyrics event.

RMID Related

Tip

See Official SF2 RMIDI Specification for more info.

embeddedSoundFont

An ArrayBuffer representation of the embedded soundfont in an RMID file. If no soundfont or not RMID, undefined. This can be either SoundFont binary or DLS binary.

Warning

If the embedded soundfont is defined, Sequencer will automatically pass it to the synthesizer. If you want to avoid this behavior, make sure you set it to undefined before passing the rmid file.

bankOffset

A number representing the bank offset of the file. Only applies to RMID, for normal MIDIs it's set to 0.

RMIDInfo

An Object representing the INFO chunk of an RMID file. See this for more information.

tracks

The actual MIDI sequence data. Described below.

Functions

MIDIticksTosecond

writeMIDIFile

Renders the sequence as a .mid file. More info

writeMIDIFile(midi);

• midi - the MIDI instance to export.

The returned value is an Uint8Array - a binary representation of the .mid file.

How the file is stored

The file is stored as an array of tracks, accesible via parsedMIDI.tracks. Each track is an array of events. Each event is a MidiMessage class, which is defined as follows;

class MidiMessage
{
  /**
   * absolute amount of MIDI Ticks from the start of the track
   * @type {number}
   */
  ticks;

  /**
   * the status byte of the message as a number from 0 to 255
   * @type {number}
   */
  messageStatusByte;

  /**
   * @type {IndexedByteArray}
   */
  messageData;
}

• ticks - absolute amount of MIDI Ticks from the start of the track.
• messageStatusByte - the status byte of the message as a number from 0 to 255. Learn more here and here.

Important

Note that for Meta Events, the status byte is the SECOND status byte, not the 0xFF!

• messageData - a IndexedByteArray(Pretty much exactly the same as Uint8Array) instance of the event's binary data.

Extracting info from midi.tracks

For a real word use-case, see how renderer calculates note times from the MIDI file.