The MIDI event stream

Feed a hardware synth over MIDI-out. Drive a stage-light show off the beat pulses. Log every note-on for post-session analysis. Anywhere you need something to happen the moment the audio plays it, subscribe to midiEventsPlayed. alphaTab surfaces every event the synthesizer sees — note-on, note-off, tempo changes, program changes, metronome ticks, and rests — filtered to only the types you asked for.

00:00 / 00:00

Filter: NoteOn, AlphaTabMetronome, TempoChange

Press play to see events…

Filter first, then subscribe

For performance, alphaTab only fires events that match midiEventsPlayedFilter. Without a filter, the event does not fire even if you subscribe. Populate the filter with entries from alphaTab.midi.MidiEventType:

• NoteOn / NoteOff — every note the synth plays.
• AlphaTabMetronome — the metronome ticks generated by alphaTab (carry beat position, subdivision, and duration).
• AlphaTabRest — synthetic events marking rests.
• TempoChange — tempo automation, useful for converting ticks to wall-clock time.
• TimeSignature, ProgramChange, ControlChange, PitchBend — for timing UIs and DAW-style integrations.

Latency and buffering

Events fire once the audio buffer has actually played them, not when they enter the synth. Expect a delay proportional to player.bufferTimeInMilliseconds — around 50 to 100 ms in a typical browser setup. If your UI needs frame-accurate feedback, keep the buffer small; if it needs stability, keep the buffer large and compensate with a lookahead.

Show it in code

import * as alphaTab from '@coderline/alphatab';

const container = getAlphaTabContainer();
const api = new alphaTab.AlphaTabApi(container, {
  core: { file: '/scores/song.gp' },
  player: {
    playerMode: alphaTab.PlayerMode.EnabledSynthesizer,
    soundFont: '/soundfont/sonivox.sf2',
  },
});

api.midiEventsPlayedFilter = [
  alphaTab.midi.MidiEventType.NoteOn,
  alphaTab.midi.MidiEventType.NoteOff,
  alphaTab.midi.MidiEventType.AlphaTabMetronome,
];

api.midiEventsPlayed.on((e) => {
  for (const event of e.events) {
    if (event.type === alphaTab.midi.MidiEventType.NoteOn) {
      console.log(`note on: key=${event.noteKey} vel=${event.noteVelocity} ch=${event.channel}`);
    } else if (event.type === alphaTab.midi.MidiEventType.NoteOff) {
      console.log(`note off: key=${event.noteKey} ch=${event.channel}`);
    } else if (event.isMetronome) {
      console.log(`metronome: beat ${event.metronomeNumerator + 1}`);
    }
  }
});

getAlphaTabContainer() is a placeholder for the platform-specific step of obtaining the render target — a <div> on Web, an AlphaTab control on .NET, or an AlphaTabView on Android. midiEventsPlayed fires with the same event shape on every runtime.

Where to look next

• Count-in and metronome — the built-in metronome that produces the AlphaTabMetronome events.
• Audio buffer size — the latency trade-off that governs event timing.
• Seeking by tick and time — the tick coordinate every event carries.
• midiEventsPlayed, midiEventsPlayedFilter, and downloadMidi in the API reference.
• MidiEventType, MidiEvent, AlphaTabMetronomeEvent, and AlphaTabRestEvent in the model reference.