Creating such a video is using the copyrighted content of others. This may or may not be copyright infringement. This is important to YouTube channel operators because the YouTube TOS states:
... the Content you submit must not include third-party intellectual property (such as copyrighted material) unless you have permission from that party or are otherwise legally entitled to do so. You are legally responsible for the Content you submit to the Service. We may use automated systems that analyze your Content to help detect infringement and abuse, such as spam, malware, and illegal content.
Youtube [Copyright Policy](https://www.youtube.com/howyoutubeworks/policies/copyright/] states:
Creators should only upload videos that they have made or that they're authorized to use. That means they should not upload videos they didn't make, or use content in their videos that someone else owns the copyright to, such as music tracks, snippets of copyrighted programs, or videos made by other users, without necessary authorizations.
Youtubne's Fair Use policy states:
Different countries have different rules about when it’s OK to use material without the copyright owner’s permission. For example, in the United States, works of commentary, criticism, research, teaching, or news reporting may be considered fair use. Some other countries have a similar concept called fair dealing that may work differently.
Courts look over potential fair use cases according to the facts of each specific case. You’ll probably want to get legal advice from an expert before uploading videos that contain copyright-protected material.
There are several possibilities.
All the other videos (source videos) have been released under a permissive license whch permits reuse, and the new video complies with any conditions specified in the license or licenses. (Such conditions probably include giving attribution, that is proper credit, to the source videos. This usually means displaying the author and title, as well as providign a link to the source.)
If this is true, the use is not copyright infringement. If this is true of only some source vids, the new vid will not be an infringement of those vids.
If all the source videos are in the public domain. This is somewhat unlikely, but possible if they are copies of films from sufficiently long ago that their copyrights expired. Also, works created by an officer or employee of the US Federal Government in the course of that person's official duties are generally in the public domain (although not if the work was created by a contractor rather than an employee. For example, many NASA vids are in the public domain.
If this is true, the use is not copyright infringement. Again, if this is true of only some source vids, the new vid will not be an infringement of those vids. No attribution is legally required for public domain vids.
If the creator of the new vid has asked for and received permission from the copyright owners of all source videos, and has complied with any conditions of those permissions. This may involve paying a fee to the source owners, and is very likely to involve proper attribution, but each owner can set whatever conditions that owner pleases.
If this is true, the use is not copyright infringement. Again, if this is true of only some source vids, the new vid will not be an infringement of those vids. However, all conditions must be carefully com,plied with.
If the creator of the new video is located in or under the jurisdiction of the US (or the copyright owner of the source is under US jurisdiction), and the creator asserts that the use is a Fair Use. Fair use is an intentionally vagus concept, and it is always decided on a case-by-case basis. Whether a use is a fair use is highly fact-based, that is the specific facts of the individual case matter a lot. Often important is whether the use will harm the market for the sourer, and whether the use is transformative. A Use is "transformative" if it is used for a significantly different purpose than the original was. Transformative uses are more likely to be considered fair uses. See Is this copyright infringement? Is it fair use? What if I don't make any money off it? and other threads tagged fair-use on this site for more details on fair use.
A fair use is not an infringement of copyright. But the only way to be sure that a ise is a fair use is to be sued in US Federal Court, raise a fair use defense, and win. A copyright lawyer can often give a reasonable opinion on whether a particular use will be considered a fair use.
A compilation video, using only short snippets of each source, might well be considered to be a fair use, but that cannot be guaranteed in general.
YouTube follows its own policies on copyright issues, including demonatization. No one else can say with assurance what YouTube will do in a particular case, particularly one near the edges of their announced policies.
