YouTube has a search filter for the CCBY license. However, you need to check if the uploader has indeed the rights to license the audio and video under that license. In some cases, you may need to uncheck "audio" when uploading to Commons using video2commons so only the CCBY-licensed video is uploaded.
Archive.org movies - Presentation of several collections of videos, some with free licenses.
Beachfront B-Roll - Personal blog offering, for free, royalty free HD stock video, High Definition and HDR time lapse clips and HD animated looping backgrounds for any personal, corporate and commercial use. Downloads are a simple "Right Click Save" and the files are hosted by Archive.org. Inactive since 2016.
Prelinger Archives - over 2,000 public domain videos of "historic significance"
Pixabay Videos - HD videos and footage released under the Pixabay license, be careful and see {{Pixabay}} for restrictions
Open Images project, an initiative from the Netherlands Institute for Sound and Vision. Many of the videos contain Dutch audio., so it's advised to remove the audio when uploading to Wikipedias other than the Dutch Wikipedia.
CuteStockFootage.com Free Videos - over 3,000 various video materials (video transitions, light leaks, particles, green screen videos, video backgrounds, etc.) - licensed under Attribution 4.0 International (CC BY 4.0)
Free Stock Video Free Stock Video Footage 4k & FULLHD Free to use, for commercial and non-commercial works.
Many studies are licensed under CCBY and include videos – with OpenAlex you can search for free media in studies but there isn't yet a filter for studies with video files (click on the + button to add a search term for the Title & Abstract)
