Library of Congress launched the National Screening Room. The National Screening Room currently offers about 300 videos. The videos are digital copies of films made in the 19th and 20th centuries. You can browse the collection by date, location of the filming, and subject. You can also search for videos that are parts of other LOC collections. All of the videos in the National Screening Room can be viewed online and or downloaded as MP4 files.

Flickr is known for hosting millions of images, but it also hosts lots of videos. how to find public domain videos on Flickr

Pixabay has been one of my go-to sites for public domain images for years. Pixabay also offers public domain video clips that you can download for free.

The Public Domain Review is a website that features collections of images, books, essays, audio recordings, and films that are in the public domain

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more on free images in this IMS blog
https://blog.stcloudstate.edu/ims?s=stock

places to find public domain images online.