What you see in this video is whole city stopping at hour "W" (5 PM) every year paying hommage to those killed in 1944 in the biggest rebellion against German Nazi occupation during WWII. Today it's 72nd anniversary of Warsaw Uprising and Warsaw will stop again for one minut in 5 hours from now. In first three days 50 000 people were killed, 200 000 in 63 days.
Another shot of hour "W":
https://www.youtube.com/watch?v=Njd0gSy4P6M