YouTube and copyright Issues

We use YouTube for watching not only short clips but also sometimes whole part of a movie.As you can find so many number of movie there ,I think by myself ,What about copy right ,"Are all the movies uploaded legally in YouTube in terms of Copy right?" and "who is responsible for this issue?" ,so for finding a proper answer to these questions .

I searched on the internet and found that; YouTube does not view videos before they are posted online, and it is left to copyright holders to issue a takedown notice under the terms of the Digital Millennium Copy Right Act which is a United States copyright law that implements two 1996 treaties of the World Intellectual Property Organization (WIPO). It criminalizes production and dissemination of technology, devices, or services intended to circumvent measures (commonly known as digital rights management or DRM) that control access to copyrighted works.

I did it further effort and tried to uploaded a clip on YouTube to test how it could be in terms of copy right issue. That was interesting to me when I saw this message ;

"Do not upload TV shows, music videos or commercials without permission," it says, "unless they consist entirely of content that you created yourself."

So ,it means sharing file in YouTube is and good opportunity ,at the same time it can breach copy right law in many cases .