i guess it would be almost impossible to copyright for example HE explosion from counter strike if you modify the pitch of the explosion sound and so on.
the copyright system is quite simple: if you are a big corporation, and anyone uses anything you ever made, even a small clip or sample for only a few seconds, you can sue the shit out of people.
if you are a small developer, you can only get fucked. do not use any copyrighted material or they will claim all your profits. and dont forget to copyright everything you make yourself, creative commons licenses are pretty affordable or even free.
so Copyright applies to "ONLY Copyrighted" Sounds,
so if there are Sounds which are "NOT Copyrighted" from any Game or whatso ever you can use it,
otherfise you can "Change the Pitch" and Copyright "WONT" apply anymore (im Coding a Game myself actualy my 2nd one right now) , but you cant just change a small pitch of it, you need to change around 40% if not, there are intelligent KI´s which will find out, BUT if you for example use an Copyrighted File , lets say a Picture or Music or whatever, you will get a Message to Remove it ASAP from your Game which means you got 1-2Days for it "MAX" or you will get fucked x),
same with 3D Models or Copyrighted "NAMES" whcih also exist, you can change it and Copyright wont Apply but you have at least to change "Enough".
goddamn my english suck, sry for that
#Edit - Videos you can USE withouth gettin Fuckt up to 14,379seconds
The whole concept of "copyright" is totally BULL, i wish you had all the right to make things the way you wanted, you have that right. Sorry for not helping with your issue, i just got a little bit mad.
why u didnt ask about it valve?