From a legal point of view I think it isn’t really grey but black & white. You can cannot use, alter, (re)publish, etx, any (protected) material from an artist without specific permission, other than for personal use (meaning car, home, etx.).
Now in practice I am guessing it depends on your succes, the tracks/artists you are using, etx.
If you upload a mix and it gets 100 hits, you’ll stay under the radar most likely. If you get thousands (or hopefully for you tens of thousands) of hits, the odds are somebody that looks out for the artist rights will notice and youtube and/or you can be summoned to take it down.
Hey, if it can make your name even if you’ll get slapped for copyright infringement, who cares, right?
Next time you’ll be so famous the artist will come to you begging to do a remix.
Greetinx,
C.
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