addStream(stream) {
    const { conf, command } = this;
    const type = conf.getVal('cacheFormat');
    command.addInput(stream);
    if (type === 'raw') command.inputFormat('rawvideo');
    this.addStreamInputOptions();
    this.inputCount++;
  }
Add the intermediate pictures processed in the cache directory to ffmpeg input
@param {Stream} stream - A readability stream
@public