May I Add A Youtuber's Free To Use Piano Music In My CS?

[Spelos]

If author allows his music to be used, I think it's perfectly fine for you to do so.

The only real problem that might arise is when someone is Let's playing your mod and the music gets flagged, this will most likely not happen, since the author publishes their work on YouTube.

All in all, I don't think the Frictional Games community will be angry with you. If the music is used well, it's quite the opposite.

I use some royalty free music from a site called incompetech.com
you are free to use his music as long as you copy the authors name and the name of the song into your credits. Be aware, though, since you need to copy the link to the licence as well, everything is in a description of each music piece.

You can also use the YouTube's Audio Library, where you can find music pieces with copyright instructions and some are even (CC0), meaning they are free to use without giving any credit at all.
There are even some really nice Foley effects, like water sounds, people coughing and such. I use some of those as well. It's intended for use in videos, but the copyright itself doesn't really say it, so feel free to use it.


And of course, you can contact your favorite indie music band, or some talent you see on YouTube and they might give you permission themselves. Many people want their music to be used, that's why they make it and all you need to do is Just ask.

Good luck in making your mod.