If you wish to use film or audio clips in your work then you need to be careful as there is very stringent copyright around these resources imposed by the ERA (Educational Recording Agency) and other bodies.
Box of Broadcasts
The best service to use for programmes and films is Box of Broadcasts. This is an off-air recording and media archive service subscribed to by the University. It allows all staff and students to choose and record any broadcast programme from 60+ TV and radio channels. The recorded programmes are then kept indefinitely (no expiry) and added to a growing media archive (currently at over 1 million programmes), with all content shared by users across all subscribing institutions.
It also allows you to record and catch-up on missed programmes on and off-campus, schedule recordings in advance, edit programmes into clips, create playlists, embed clips into ELE, share what you are watching with others, and search the growing archive of material.
If you want to know more get in touch by email email@example.com.
There is a wealth of material on YouTube and it is very easy to copy and paste from however some of it is plagiarised, some of it is copyrighted and some of it is perfectly legal to use.
YouTube does not become involved in rights ownership disputes, so it is your responsibility to determine whether it is legal to use specific content. Therefore, if you are not the owner of the film or are unable to ascertain whether its use is legal, do not use it.
YouTube have a large section on copyright if you wish to find out more: http://www.youtube.com/yt/copyright/en-GB/