Copyright

Copyright attaches to an original work as soon as it exists in a fixed form, with no registration, notice or filing required in the countries that signed the Berne Convention. It covers the expression rather than the underlying idea, so two people can make videos about the same subject, and neither can use the other's footage, script or edit. Registration is a different matter. In some jurisdictions it changes what you can sue for, but the right itself exists without it. Nearly every YouTube dispute traces back here: a claim, a takedown and a strike are all downstream of somebody owning a work you used.