Copyright on video game montages, commentries etc?

[Louis]

whats the copyright rules around recording gameplay and making a montage or adding commentry over it on youtube and other video sites?
Because im a partner and i have to keep my slate clean of copyright issues and all the stuff about it has to be your own artwork ect
And i know there are thousands out there but is it actually legal?

Thanks

[DefaultHumanBeing]

If its not your own Gameplay or commentary and you use it without user permission then its plagarism and you can be sued if it can be proved.