music/song and copyright on Youtube/videos

 For musics and copyright on a Youtube video, you must need to be eligible even if its a small part of the song, needing permission by the creator or author. For a song on a video usually is needed an official music license letting you the rights to use it. when having it read your license, because of such limitations, that if they are not followed might have a cost. I think that when using a song, read all the terms and policy, to see if has a cost or a type of permission and/or limitation. Also when creating a song or sound check well, because can bring problems by having the same sound even if its a little of a similar sound might bring problems.