This domain is part of Google's backend infrastructure for YouTube. When you watch a video, your device connects to servers like this one to stream content. The 404 page you see when visiting directly is normal — these servers aren't meant for browsing.
Is r5---sn-hp57ynse.googlevideo.com a scam? No. The server is hosted on Google's own network, uses a valid SSL certificate from Google Trust Services, and has no blacklist or security warnings. The domain is a subdomain of googlevideo.com, which is a verified Google property.
Because this is not a commercial site, the absence of contact info, legal pages, and social media are all expected. For anyone concerned about safety, the signals point firmly to legitimate infrastructure. There's no reason to treat this server as suspicious. It simply does what it's built to do: serve YouTube video data reliably and securely.