@dawcore/transport

Native Web Audio transport for multi-track audio scheduling, looping, tempo, and metronome. Zero npm dependencies.

Features

• Native Web Audio — No Tone.js, no standardized-audio-context. Direct AudioContext with full sampleRate and latencyHint control.
• Sliding window scheduler — Schedules audio 200ms ahead via requestAnimationFrame for glitch-free playback.
• Dual timeline — Sample-absolute positions for audio clips, PPQN tick positions for metronome/MIDI.
• Built-in metronome — Beat-grid click scheduling with accent on beat 1. Default synthesized click sounds out of the box.
• Count-in (pre-roll) — Configurable bars of click sounds before playback begins. Beat-by-beat events for UI countdown.
• Per-track signal chain — Native GainNode (volume) → StereoPannerNode → GainNode (mute) → effects hook → master output.
• Effects plugin hook — connectTrackOutput(trackId, node) inserts any AudioNode chain (Tone.js effects, WAM plugins, native nodes).
• Type-safe coordinates — Branded Tick and Sample types prevent accidentally passing seconds where ticks or samples are expected. Zero runtime cost.
• PlayoutAdapter bridge — NativePlayoutAdapter implements the PlayoutAdapter interface from @waveform-playlist/engine.

Installation

npm install @dawcore/transport

Peer dependencies:

npm install @waveform-playlist/core @waveform-playlist/engine

Quick Start

Standalone Transport

import { Transport } from '@dawcore/transport';

const audioContext = new AudioContext({ sampleRate: 48000, latencyHint: 0 });
const transport = new Transport(audioContext, { tempo: 120 });

transport.setTracks([
  {
    id: 'drums',
    name: 'Drums',
    clips: [{ id: 'clip-1', audioBuffer: drumBuffer, startSample: 0, durationSamples: 48000, offsetSamples: 0, sampleRate: 48000, sourceDurationSamples: 48000, gain: 1 }],
    volume: 1,
    pan: 0,
    muted: false,
    soloed: false,
  },
]);

transport.play();

With PlaylistEngine (dawcore)

import { NativePlayoutAdapter } from '@dawcore/transport';

const audioContext = new AudioContext({ sampleRate: 48000 });
const adapter = new NativePlayoutAdapter(audioContext);

// Use as daw-editor's adapter factory
const editor = document.querySelector('daw-editor');
editor.adapterFactory = () => new NativePlayoutAdapter(audioContext);

Metronome

const transport = new Transport(audioContext, {
  tempo: 120,
  numerator: 4,
  denominator: 4,
});

// Default click sounds are built in — just enable and play
transport.setMetronomeEnabled(true);
transport.play();

// Override with custom click sounds
transport.setMetronomeClickSounds(accentBuffer, normalBuffer);

Count-In

transport.setCountIn(true);
transport.setCountInBars(1);           // 1–8 bars, default 1
transport.setCountInMode('always');    // 'always' | 'recording-only' (default)

// Beat-by-beat events for UI countdown
transport.on('countIn', ({ beat, totalBeats }) => {
  console.log(beat + ' / ' + totalBeats);  // "1 / 4", "2 / 4", ...
});

transport.on('countInEnd', () => {
  console.log('Playback starting');
});

transport.play();  // Plays count-in clicks, then starts playback

Mixed Meter

const transport = new Transport(audioContext, { tempo: 120, numerator: 4, denominator: 4 });

// Switch to 7/8 at bar 5
transport.setMeter(7, 8, transport.barToTick(5));

// Query active meter at any tick
const { numerator, denominator } = transport.getMeter(transport.barToTick(5));
// → { numerator: 7, denominator: 8 }

transport.setMetronomeEnabled(true);
transport.play();

Tempo Automation

const transport = new Transport(audioContext, { tempo: 100 });

// Linear ramp from 100 to 160 BPM over 8 bars
transport.setTempo(160, transport.barToTick(9), { interpolation: 'linear' });

// Query interpolated BPM at any position
transport.getTempo(transport.barToTick(5)); // 130 BPM (midway through ramp)

// Curved ramp: ease-in (slow start, fast end)
transport.clearTempos();
transport.setTempo(80);
transport.setTempo(160, transport.barToTick(9), {
  interpolation: { type: 'curve', slope: 0.2 },  // concave
});

// Curved ramp: ease-out (fast start, slow end)
transport.clearTempos();
transport.setTempo(80);
transport.setTempo(160, transport.barToTick(9), {
  interpolation: { type: 'curve', slope: 0.8 },  // convex
});

// Mix step and linear: jump to 80 BPM at bar 4, ramp to 140 at bar 8
transport.clearTempos();
transport.setTempo(120);
transport.setTempo(80, transport.barToTick(5));  // step (instant jump)
transport.setTempo(140, transport.barToTick(9), { interpolation: 'linear' });  // ramp

Effects

// Insert any AudioNode chain between track output and master
const reverb = audioContext.createConvolver();
reverb.buffer = impulseResponse;
reverb.connect(transport.audioContext.destination);

transport.connectTrackOutput('vocals', reverb);

// Remove effects — restores direct routing to master
transport.disconnectTrackOutput('vocals');

API

Transport

new Transport(audioContext: AudioContext, options?: TransportOptions)

TransportOptions: | Option | Default | Description | |--------|---------|-------------| | sampleRate | audioContext.sampleRate | Sample rate for timeline conversions | | ppqn | 960 | Ticks per quarter note | | tempo | 120 | Initial tempo in BPM | | numerator | 4 | Beats per bar (time signature numerator) | | denominator | 4 | Beat unit (time signature denominator) | | schedulerLookahead | 0.2 | How far ahead to schedule (seconds) | | accentFrequency | 1000 | Default accent click frequency (Hz) | | normalFrequency | 800 | Default normal click frequency (Hz) |

Playback:

• play(startTime?, endTime?) — Start or resume playback
• pause() — Pause, preserving position
• stop() — Stop and reset to beginning
• seek(time) — Jump to a position (works during playback)
• getCurrentTime() — Current transport position in seconds
• isPlaying() — Whether transport is playing

Tracks:

• setTracks(tracks) — Set all tracks (rebuilds audio graph)
• addTrack(track) — Add a single track
• removeTrack(trackId) — Remove a track
• updateTrack(trackId, track) — Update a track's clips

Track Controls:

• setTrackVolume(trackId, volume)
• setTrackPan(trackId, pan)
• setTrackMute(trackId, muted)
• setTrackSolo(trackId, soloed)
• setMasterVolume(volume)

Loop:

• setLoop(enabled, startTick: Tick, endTick: Tick) — Set loop region in ticks (primary API)
• setLoopSeconds(enabled, start, end) — Set loop region in seconds (convenience)
• setLoopSamples(enabled, startSample: Sample, endSample: Sample) — Set loop region in samples (convenience)

Tempo & Meter:

• setTempo(bpm, atTick?, options?) / getTempo(atTick?: Tick) — options: { interpolation: 'step' | 'linear' | { type: 'curve', slope } }
• clearTempos() — remove all tempo entries
• setMeter(numerator, denominator, atTick?: Tick) / getMeter(atTick?: Tick)
• removeMeter(atTick: Tick) / clearMeters()
• barToTick(bar): Tick / tickToBar(tick: Tick)
• timeToTick(seconds): Tick / tickToTime(tick: Tick)

Metronome:

• setMetronomeEnabled(enabled)
• setMetronomeClickSounds(accent, normal) — overrides default synthesized sounds

Count-In:

• setCountIn(enabled) — enable/disable count-in
• setCountInBars(bars) — number of bars (1–8, default 1)
• setCountInMode(mode) — 'recording-only' (default) or 'always'
• setRecording(recording) — consumer signals recording state (for 'recording-only' mode)
• isCountingIn() — whether count-in is active

Effects:

• connectTrackOutput(trackId, node) — Insert effects chain
• disconnectTrackOutput(trackId) — Remove effects chain

Events:

• on(event, callback) / off(event, callback)
• Events: play, pause, stop, loop, tempochange, meterchange, countIn, countInEnd
• tempochange payload: { bpm: number, atTick: Tick }
• meterchange payload: { numerator: number, denominator: number, atTick: Tick }
• countIn payload: { beat: number, totalBeats: number }

Cleanup:

• dispose() — Stop playback, disconnect all nodes, remove listeners

NativePlayoutAdapter

new NativePlayoutAdapter(audioContext: AudioContext, options?: TransportOptions)

Implements PlayoutAdapter from @waveform-playlist/engine. All methods delegate to the internal Transport instance.

• adapter.transport — Direct access to the Transport for tempo, metronome, and effects APIs

Architecture

See TRANSPORT.md for the full architecture guide.

How It Works

See EDUCATIONAL.md for an in-depth explanation of the math and timing models behind audio transport systems.

License

MIT