A lot of people upload game music there and I was wondering, is it illegal or not? Am I doing copyright infringement while listening to it and thus, stealing?
If anyone is guilty of illegal activity it’s who uploaded it in the first place. And that is carefully monitored by YouTube’s algorithms with the copyright owner notified. If they then choose not to get it taken down, you, and the uploader are definitely in the clear.
I once uploaded my VFX showreel with a copyrighted piece of music on it as its soundtrack. The creators of that music were notified but they allowed it, presumably considering it harmless usage.
So it’s not copyright infringement?
To listen to something somebody else has uploaded? No. To possess, possibly, though it can depend on what you intend to do with it.
To elaborate a bit on GuanoLad’s answers:
For you? No. Copyright infringement requires you to distribute the work. You haven’t done so, so you’re in the clear.
For the uploader? Yes, technically. So if a company wanted to, they could force it to be taken down. But they can also decide they don’t care. It is unlikely that listening to music is going to keep people from buying the games, so most let it slide.
The exception would be if the game developer has explicitly given permission. Then it would not be copyright infringement. You would be using it by permission.
That said, if any of them sell the music on iTunes or something, they might decide they don’t want you listening to the music for free and take down the YouTube videos. Or they may just put some ads on it and get some money out of that.
However, the point is, you do not have to worry about anything. You’re just listening to the music. That is definitely not copyright infringement.