createStream() {
    const conf = this.rootConf();
    const size = conf.getVal('highWaterMark');
    const parallel = conf.getVal('parallel');

    const stream = new FFStream({ size, parallel });
    stream.addPullFunc(this.renderFrame.bind(this));
    stream.on('error', error => this.emitError({ error, pos: 'FFStream' }));
    this.stream = stream;
  }
Create a stream pipeline for data transmission
@private