Add tracks or create new Stream ending with Media Recorder ending up corrupted file

this is the last post which answer where my goal is in developing my project: RecordRTC with sending video chunks to server and record as webm or mp4 on server side. After recording the screen sharing stream, I decide to move forward to add video tracks to screen sharing. There are two ways for me to do it, by using addTracks function or create a new stream with contain the video from the screen sharing and audio from my media. However, both of them resulting me in the previous error in the aforementioned link: corrupted video.

FYI: Here is the link for anyone who wants to read more about Media Recorder: https://developer.mozilla.org/en-US/docs/Web/API/MediaRecorder

P/S: If you encourage me on switching to webRTC again, I would be appreciated if you could help me in solving the issue - the file ends up corrupted when using webRTC - in aforementioned link?

Here is the code from my backend and frontend:

Client code:

startMedia = ()=>{
      this.setState({mediaState:"pending"})
      navigator.mediaDevices.getDisplayMedia({video: true}).then( async (screenSharingStream)=>{
          console.log(MediaRecorder.isTypeSupported('video/webm; codecs=vp8,opus'))
          const socketIO = io.connect(baseURL,{query: {candidateID: this.candidateID,roundTest:this.roundTest }})
          const mediaStream = await navigator.mediaDevices.getUserMedia({video:true,audio:true}).catch(e => {throw e});
          const mediaReCorderoptions = {
            videoBitsPerSecond : 128000,
            audioBitsPerSecond:128000,
            mimeType : 'video/webm; codecs=vp8,opus'
          }
          
          const [videoTrack] = screenSharingStream.getVideoTracks();
          const [audioTrack] = mediaStream.getAudioTracks();
          if (audioTrack && videoTrack) 
            videoTrack.addTrack(audioTrack)
          
          const stream = new MediaStream([videoTrack, audioTrack]);
          this.socketRef.current = socketIO;
          this.mediaStream = mediaStream

          this.screenSharingStream = stream 
          this.candidateVideoRef.current.srcObject = this.mediaStream;
          this.mediaRecorder = new MediaRecorder(this.screenSharingStream,mediaReCorderoptions)
          this.mediaRecorder.ondataavailable = function(event){
            if (event && event.data.size>0){
              const reader = new FileReader();
              reader.onload = function(){
                const dataURL = reader.result;
                console.log('van chay')
                const base64EncodedData = dataURL.split(',')[1];
                //console.log(buffer)
                socketIO.emit('SEND BLOB',base64EncodedData)
              }
              reader.readAsDataURL(event.data)
            }
          }
          this.mediaRecorder.start(1000)
          this.setState({mediaState:this.mediaRecorder.state})

                  

      }).catch(err=>{
          console.log(err.name)
          switch(err.name){
            case 'NotAllowedError':
              message.error('Candidate does not allow!!')
              this.setState({mediaState:"Aborting"})
              break;
            default:
              message.error('System Error. Please contact us!')
              this.setState({mediaState:"Aborting"})
              break;
          }
      })
    
  }
  stopMedia = () =>{
      if (this.mediaStream){
        this.mediaStream.getTracks().forEach((track)=>{
          if (track.readyState==='live') {
            track.stop()
            this.candidateVideoRef.current.style.display='none';
          }})
      }
      if (this.screenSharingStream) {
        this.mediaRecorder.stop()
        this.setState({mediaState:this.mediaRecorder.state})
      }
  }

Server code:

socket.on("SEND BLOB",chunk=>{
        try {
        //if (chunk instanceof Buffer){
            const fileExtension = '.webm'
            const  dataBuffer = new Buffer(chunk, 'base64');
            const fileStream = fs.createWriteStream(path.join(__dirname,'./videos/candidate/',candidateID + '-' + roundTest + fileExtension), {flags: 'a'});
            fileStream.write(dataBuffer);
        }
        catch(e){
            console.log(e)
        }
})