Help Understanding YouTube and Copyright Laws?

[bcnu]

You, like the person who uploaded the video or music, would absolutely need a license from the copyright owners in order to duplicate and distribute (i.e., upload) any copies of those copyrighted works, assuming you don't want to be sued.

in a FEW countries, under "fair dealing" laws, you can get away with publishing up to 30 seconds of some music in an effort to advertise sales of authorized copies. The USA is not one of those countries; there is no legal "minimum", and people have been successfully sued for violating less than 5 seconds of music.