setHighWaterMark({ command, highWaterMark }) {
    highWaterMark = siz(highWaterMark);
    command.ffmpegProc.stdin._writableState.highWaterMark = highWaterMark;
    command.ffmpegProc.stdin._readableState.highWaterMark = highWaterMark;
  }
Set a water mark for swpan stdin

@param {number} highWaterMark - a water mark for swpan stdin
@public