This was shot in a small town in Serbia, as the witness reports, "above Lepenski Vir." (Should say "In the direction of Lepenski Vir." There is no way to determine how far away the objects were.) Lepenski Vir is an important mesolithic archaeological site dating back to around 9,000BC.
The triangular formation in the video is typical of such formations. It is not a triangular object, but a group of bright objects that form into a triangle, then wink out one by one.