It is all kind of odd things and also perfect for music videos and of course there is a lot of great samples to be found. Really recommendable to go and take a look. The danger is that hours will be lost as there is a lot and all more or less exciting...
https://www-muehlen.archive.org/details/prelinger&tab=collection
Here is what is said about usage of the material:
You are warmly encouraged to download, use and reproduce these films in
whole or in part, in any medium or market throughout the world. You are
also warmly encouraged to share, exchange, redistribute, transfer and copy
these films, and especially encouraged to do so for free.
Any derivative works that you produce using these films are yours to
perform, publish, reproduce, sell, or distribute in any way you wish
without any limitations.