Internationally speaking, the concept of fair use, where a content creator can use a copyright holder's content without any civil or criminal penalties, hinges on how much the original content was transformed.
Put in other words, if you were just to take somebody's work and just cut it up, that is not enough of a transformation for your derivative content to qualify under the fair use exemption of international copyright law.
This is where commentary comes in.
If you've ever watched those annoying YouTube channels of people just blabbering on you can see gameplay footage, it's actually the chatter that converts what would otherwise be the property of a video game publisher into fair use content.
This content can be monetized.
This content can be published.
This content, for all intents and purposes, is the property of the creator and not necessarily the copyright holder.
But this goes out the window if you come up with no-commentary game footage.
At the very best, Google might take whatever monetization that could've gone to you and give it to the right's owner.
That does happen, especially when it comes to music.
At worst, your stuff can get taken down.
This is why it's really a good idea to focus on commentary.
How do you make somebody else's otherwise copyrighted work your own?
Well, you can do it through commentary.
You can do it through certain types of derivative content.
You can do mashups.
You also have to understand that YouTube can be too touchy with what you can get away with when it comes to copyright issues.
I remember seeing a lot of comedy channels where people just basically show themselves on one side of the screen laughing at the jokes being cracked by a comedian and the segment is from Comedy Central.
A lot of them get away with this, but many do get flagged.
So it's kind of a touch and go.
These types of "reaction videos" might not transform the content enough for it to qualify as "fair use" so consider yourself warned.
I wouldn't want you to go through all the time and effort of putting together a no-commentary game channel that managed to get an organic community going and by the time you get thousands upon thousands of subscribers, you get dinged with demonetization, or worse yet, your channel gets shut down.