constructor(conf) {
    super();

    this.conf = conf;
    this.cover = null;
    this.audios = null;
    this.duration = 0;
    this.inputCount = 0;
    this.framesNum = 100;
    this.outputOptions = [];
    const threads = conf.getVal('threads');
    this.command = FFmpegUtil.createCommand({ threads });
  }
Synthesis - A class for video synthesis.
Mainly rely on the function of ffmpeg to synthesize video and audio.

####Example:

    const synthesis = new Synthesis(conf);
    synthesis.addStream(stream);
    synthesis.addAudios(audios);
    synthesis.start();


@class