API Reference

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API Reference / createRealtimeBpmAnalyzer

Function: createRealtimeBpmAnalyzer()

function createRealtimeBpmAnalyzer(audioContext, processorOptions?): Promise<BpmAnalyzer>;

Defined in: index.ts:131

Creates a real-time BPM analyzer for live audio streams.

This function sets up a BPM analyzer that processes audio in real-time to detect the beats-per-minute (tempo) of streaming audio sources like microphones, audio elements, or live streams.

Parameters

Parameter	Type	Description
audioContext	AudioContext	The Web Audio API AudioContext to use for processing
processorOptions?	RealTimeBpmAnalyzerParameters	Optional configuration parameters for the analyzer

Returns

Promise<BpmAnalyzer>

A promise that resolves to a BpmAnalyzer instance (event emitter wrapping AudioWorkletNode)

Remarks

The returned BpmAnalyzer is an event emitter that wraps an AudioWorkletNode.

• Use the analyzer directly for event listening: analyzer.on('bpm', ...)
• Use .node property for Web Audio API connections: source.connect(analyzer.node)

Examples

Basic Usage with Audio Element

const audioContext = new AudioContext();
const bpmAnalyzer = await createRealtimeBpmAnalyzer(audioContext);

// Connect audio graph - use .node for AudioWorkletNode connections
const audioElement = document.querySelector('audio');
const source = audioContext.createMediaElementSource(audioElement);
source.connect(bpmAnalyzer.node);
bpmAnalyzer.node.connect(audioContext.destination);

// Listen for BPM events with full type safety
bpmAnalyzer.on('bpm', (data) => {
  console.log('Current BPM:', data.bpm[0].tempo);
  console.log('Confidence:', data.bpm[0].count);
});

bpmAnalyzer.on('bpmStable', (data) => {
  console.log('Stable BPM detected:', data.bpm[0].tempo);
});

With Custom Configuration

const audioContext = new AudioContext();
const bpmAnalyzer = await createRealtimeBpmAnalyzer(audioContext, {
  continuousAnalysis: true,    // Keep analyzing after stable BPM found
  stabilizationTime: 20000,    // Time in ms to consider BPM stable
  muteTimeInIndexes: 10000,    // Audio indexes to skip between peaks
  debug: false                 // Enable debug logging
});

With Microphone

const audioContext = new AudioContext();
const bpmAnalyzer = await createRealtimeBpmAnalyzer(audioContext);

// Connect microphone - use .node for audio connections
const stream = await navigator.mediaDevices.getUserMedia({ audio: true });
const source = audioContext.createMediaStreamSource(stream);
source.connect(bpmAnalyzer.node);
// Note: Don't connect to destination to avoid feedback

// Handle different event types
bpmAnalyzer.on('bpm', (data) => {
  console.log('Analyzing:', data.bpm[0].tempo);
});

bpmAnalyzer.on('bpmStable', (data) => {
  console.log('Stable BPM:', data.bpm[0].tempo);
  console.log('Confidence:', data.bpm[0].count);
});

// One-time listener
bpmAnalyzer.once('bpmStable', (data) => {
  console.log('First stable detection!');
});

Controlling the Analyzer

// Reset the analyzer state
bpmAnalyzer.reset();

// Listen for reset events
bpmAnalyzer.on('analyzerReset', () => {
  console.log('Analyzer was reset');
});

// Stop the analyzer
bpmAnalyzer.stop();

// Remove listeners with native API
const handler = (event) => console.log(event.detail);
bpmAnalyzer.addEventListener('bpm', handler);
bpmAnalyzer.removeEventListener('bpm', handler);

// Or use once() for automatic cleanup
bpmAnalyzer.once('bpmStable', (data) => console.log('First detection'));

// Disconnect and cleanup
bpmAnalyzer.disconnect();

See

• BpmAnalyzer for the analyzer class API
• analyzeFullBuffer for offline audio file analysis
• RealTimeBpmAnalyzerParameters for configuration options
• BpmCandidates for the structure of BPM results