Hey if you guys need some information on this sort of stuff, there are some resources on the web. Did a little Googling around and found this:
"In order to use a musical composition in a movie, you need to get a license from the PA copyright owner(s). In order to use a specific recording of a song, you need to get a sync license from the copyright owner of the sound recording as well as rights for the musical composition from the publishing company and writer/composer who administer the PA. Using the above example, permission to use the Frank Sinatra version of released by Reprise for use in Mrs. Doubtfire would be granted by Reprise Records for the SR, Frank Loesser and his Publisher for the PA. Synch Fees would be collected for this use (performance royalties would be collected and distributed as well as Mrs. Doubfire broadcasted) by the label and publisher(s). Making a new recording from a well-known musical composition for a movie is not uncommon because it can be less expensive than licensing the original recording for the sound recording copyright holder. Using a popular recording in a movie can sometimes cost well over $100,000."
Replace "movie" with "YouTube video" and I'm sure terms are similar. Got it from my friend who writes blog content for Muserk. Hope that helps!