- Mixes: I ask the artists for permission and also request a brief on the license details for the song, to include it on the description. They often have "more restrictive" licenses (like asking the author for usage).
- Compilations: They're always royalty-free music, from us, NCS or other similar channels. You can assume the tracks can be used as long as credit is given in the same way I gave credit on my description.
In both cases, our solution is point you to the description. You're going to find something like this:
Tracklist + Credits (below)
PS: I would contact the artist of the song you want to use, if you're still unsure.