Pipe live stream from NodeJS Readable to ffmpeg

I am using Twilio for transfering audio calls to a meeting room on top of Mediasoup. Using Twilio websocket I get media stream encoded in base64 and push that to a NodeJS Readable stream. Then I will pipe that readable stream to a ffmpeg process I created before, using NodeJS spawn()

The problem is that only 92 bytes pipes into ffmpeg and so the output is not playable. I dont have any idea if the options of ffmpeg is wrong or I'm using Readable stream bad way.

const process = spawn('ffmpeg', [
      '-loglevel',
      'debug',
      '-re',
      '-protocol_whitelist',
      'pipe,udp,rtp',
      '-f',
      'mulaw',
      '-i',
      'pipe:0',
      '-map',
      '0:a',
      '-c:a',
      'pcm_mulaw',
      'output.wav'
    ]);

const rstream = new Readable({ encoding: 'binary' })
rstream._read = () => {};

rstream.resume();
rstream.pipe(process.stdin)

each time I get media from Twilio socket as base64, I push that chunk into rstream using:

const mediaBytes = Buffer.from(base64Chunk, "base64")
const count = mediaBytes.byteLength

rstream.push(Buffer.from([0x52, 0x49, ... /* PCM MU_LAW HEADER 54 Bytes */]))
rstream.push(Buffer.from([
          count % 256,
          (count >> 8) % 256,
          (count >> 16) % 256,
          (count >> 24) % 256,
        ]))
rstream.push(mediaBytes)