StreamMixer helps to play with MediaStream: Merge multiple streams into single one ( can be used with WebRtc to send multiple streams over a single WebRTC MediaConnection, or to switch streams without worrying about renegotiation)

StreamMixer.ts

export class StreamMixer {
  streams: Array<{
    id: string,
    audioSource: any,
    gainNode: any,
    mediaStream: MediaStream
  }>;
  destination: any;
  audioCtx: any;

  constructor() {
    this.streams = [];
    this.audioCtx = new AudioContext();
    this.destination = this.audioCtx.createMediaStreamDestination();
  }

  get stream() {
    return this.destination.stream;
  }

  addStream(mediaStream): void {
    try {
      const id = mediaStream.id;
      const audioSource = this.audioCtx.createMediaStreamSource(mediaStream);
      const gainNode = this.audioCtx.createGain();
      audioSource.connect(gainNode);
      gainNode.connect(this.destination);
      this.streams.push({ id, audioSource, gainNode, mediaStream });
    } catch (e) {
      console.error(e);
    }

  }

  removeStream(mediaStream): void  {
    for (let i = 0; i < this.streams.length; i++) {
      if (this.streams[i].id == mediaStream.id) {
        this.streams[i].audioSource = null;
        this.streams[i].gainNode.disconnect(this.destination);
        this.streams[i].gainNode = null;
        this.streams[i] = null;
        this.streams.splice(i, 1);
      }
    }
  }
}