recorder.worklet.js

class RecorderProcessor extends AudioWorkletProcessor {
    // 0. Determine the buffer size (this is the same as the 1st argument of ScriptProcessor)
    bufferSize = 16384
    // 1. Track the current buffer fill level
    _bytesWritten = 0

    // 2. Create a buffer of fixed size
    _buffer = new Float32Array(this.bufferSize)

    constructor() {
        super()
        this.initBuffer()
    }

    initBuffer() {
        this._bytesWritten = 0
    }

    isBufferEmpty() {
        return this._bytesWritten === 0
    }

    isBufferFull() {
        return this._bytesWritten === this.bufferSize
    }

    /**
   * @param {Float32Array[][]} inputs
   * @returns {boolean}
   */
    process(inputs) {
        // Grabbing the 1st channel similar to ScriptProcessorNode
        this.append(inputs[0][0])

        return true
    }

    /**
     *
     * @param {Float32Array} channelData
     */
    append(channelData) {
        if (this.isBufferFull()) {
            this.flush()
        }

        if (!channelData) return

        for (let i = 0; i < channelData.length; i++) {
            this._buffer[this._bytesWritten++] = channelData[i]
        }
    }

    flush() {
        // trim the buffer if ended prematurely
        this.port.postMessage(
            this._bytesWritten < this.bufferSize
                ? this._buffer.slice(0, this._bytesWritten)
                : this._buffer
        )
        this.initBuffer()
    }

}

registerProcessor("recorder.worklet", RecorderProcessor)