Brazilian news portal G1 reports that this footage was captured by 20-year-old web designer Erick Reis as he was leaving a friend's engagement party this past Sunday. G1 spoke with a local biologist who identified the spider as Anelosimus eximius — a "social spider" species known for its massive colonies and "sheet webs." He characterized the phenomenon as "normal," which it most certainly is not. (From YouTube description)