Record web audio to an MP3 in mono or stereo.

Live demo.

Supports all modern browsers.

    import { Mp3Recorder } from './src/Mp3Recorder.mjs';

    let recorder = new Mp3Recorder();

    await recorder.configure(inputAudioNode, channels, bitRate);

    recorder.start();

    recorder.pause();

    recorder.resume();

    let bytes = await recorder.getRecordedSize();

    let mp3 = await recorder.stop();

Copy the files in src into your project.

• Mp3RecorderWorklet.js: tiny AudioWorkletProcessor that feeds raw audio to the worker.
• Mp3RecorderWorker.js: encodes audio in real time (using lamejs, inline in the file). We use a separate worker to avoid dropping frames during encoding (AudioWorkletProcessor has hard coded 128 byte buffer).
• Mp3Recorder.mjs: coordinates worker threads and provides an API for them. This is what you use in your code. The other files are necessary evils because of the way web threading works.

Mp3Recorder()

You should only create one instance of Mp3Recorder to avoid proliferation of worker threads.

async configure(inputNode, channels, bitRate):

This can be called as many times as you want to change the audio node being recorded or to reconfigure the encoder.

• inputNode: the AudioNode whose output we'll record
• channels: 1 or 2 (mono or stereo)
• bitRate: bit rate to encode at

start()

Start recording.

pause()

Pause recording.

resume()

Resume recording after it's been paused.

async getRecordedSize()

Return the number of bytes recorded so far.

async stop()

Stop recording and return the MP3 blob.