stack-chan

import AudioIn from 'embedded:io/audio/in'

export default class Microphone {
  recording: boolean

  constructor() {
    this.recording = false
  }

  async record(durationMilliSec = 3000): Promise<ArrayBuffer> {
    if (this.recording) {
      throw new Error('already recording')
    }
    this.recording = true
    const HEADER_SIZE = 44

    return new Promise((resolve) => {
      let writeOffset = 0
      const audioin = new AudioIn({
        onReadable(size) {
          const remaining = dataView.byteLength - writeOffset
          trace(`${remaining}\n`)
          const chunkSize = Math.min(size, remaining)
          const chunk = this.read(chunkSize)

          if (!chunk) {
            this.close()
            resolve(wavBuffer)
          } else {
            dataView.set(new Uint8Array(chunk), writeOffset)
            writeOffset += chunkSize
            if (writeOffset >= dataView.byteLength) {
              this.close()
              resolve(wavBuffer)
            }
          }
        },
      })

      // generate header
      const { sampleRate, channels, bitsPerSample } = audioin
      const byteRate = sampleRate * channels * (bitsPerSample >> 3)
      const contentLength = (durationMilliSec / 1000) * byteRate
      const wavBuffer = new ArrayBuffer(HEADER_SIZE + contentLength)
      const headerView = new DataView(wavBuffer)
      const dataView = new Uint8Array(wavBuffer, HEADER_SIZE)

      headerView.setUint8(0, 'R'.charCodeAt(0))
      headerView.setUint8(1, 'I'.charCodeAt(0))
      headerView.setUint8(2, 'F'.charCodeAt(0))
      headerView.setUint8(3, 'F'.charCodeAt(0))
      headerView.setUint32(4, 36 + contentLength, true)
      headerView.setUint8(8, 'W'.charCodeAt(0))
      headerView.setUint8(9, 'A'.charCodeAt(0))
      headerView.setUint8(10, 'V'.charCodeAt(0))
      headerView.setUint8(11, 'E'.charCodeAt(0))
      headerView.setUint8(12, 'f'.charCodeAt(0))
      headerView.setUint8(13, 'm'.charCodeAt(0))
      headerView.setUint8(14, 't'.charCodeAt(0))
      headerView.setUint8(15, ' '.charCodeAt(0))
      headerView.setUint32(16, 16, true)
      headerView.setUint16(20, 1, true) // AudioFormat = 1 (PCM)
      headerView.setUint16(22, channels, true)
      headerView.setUint32(24, sampleRate, true)
      headerView.setUint32(28, byteRate, true)
      headerView.setUint16(32, (channels * bitsPerSample) >> 3, true)
      headerView.setUint16(34, bitsPerSample, true)
      headerView.setUint8(36, 'd'.charCodeAt(0))
      headerView.setUint8(37, 'a'.charCodeAt(0))
      headerView.setUint8(38, 't'.charCodeAt(0))
      headerView.setUint8(39, 'a'.charCodeAt(0))
      headerView.setUint32(40, contentLength, true)

      // start recording
      audioin.start()
    })
  }
}