I do not care about moral code.

For IP laws, copyright law will be intrested in your activities.

There is exception to copyright law in US called fair use(YT also says fair use) in other places it is also called fair dealing. The idea in theory is that if your content is "transformative" in nature, then it is fair use and does not violate the copyright law.

How will you know if a content is transformative?

If you change the content significantly, like satire, commenatry, etc. it becomes tranformative. The crux is the content has to transform in its meaning from the copied content so as to not be an alternative to the original. Well some courts interpret it different but fair use is interpreted broadly so as to not hamper new creation of art and science.

Gathering stock footage from yt sounds okay to me, you will put in the works to edit those cut those clean audio, choose which clips to use etc. At this point I would argue it is transformative. If you do not intend to earn from the clips then it is valid use.

Also copyright law depends on the claimant of the contents, think of it like, you have not broken the law untill someone has raised the claim.(Over simplification). If no one claimed the copyright well it's alright. [The last para is my philosophy in IP, may be I am wrong]

This is not a legal advice. Research more. IP law is complicated. Ask more if you wanna know more, will help as much as I can.