Function not exported in liveMedia555 vs 2019

I cloned the LiveMedia555 repository on https://github.com/rgaufman/live555 and I've created a solution in VS2019. I built solution under Windows target platform version 81, vc140. My output is a static library .lib. I linked this lib in another project that uses LiveMedia but when I compile this project I've many link errors like

error LNK2001: unresolved external symbol "private: virtual void __cdecl MultiFramedRTPSource::doGetNextFrame(void)" (?doGetNextFrame@MultiFramedRTPSource@@EEAAXXZ)

the above function is in liveMedia and its code is

void MultiFramedRTPSource::doGetNextFrame() {
  if (!fAreDoingNetworkReads) {
    // Turn on background read handling of incoming packets:
    fAreDoingNetworkReads = True;
    TaskScheduler::BackgroundHandlerProc* handler
      = (TaskScheduler::BackgroundHandlerProc*)&networkReadHandler;
    fRTPInterface.startNetworkReading(handler);
  }

  fSavedTo = fTo;
  fSavedMaxSize = fMaxSize;
  fFrameSize = 0; // for now
  fNeedDelivery = True;
  doGetNextFrame1();
}

Where can I wrong?