CITATION HELP, FAST!
Just because it's visible on the Internet, does NOT mean it's free for anyone to use in any way.
Avoiding plagiarism:
Public Domain: Works in the public domain are not protected by copyright and can be used freely. Examples of works in public domain:
Note: It is common practice in academia to give credit, even when using material in the public domain.
Converting the file format of audio and video recordings is completely forbidden by copyright law at this time. In order to use any excerpts in class or classwork which do not come directly (during use) from the original purchased recording, written permission must be obtained from the copyright owner.
There is NO Fair Use exemption for this law.
The safest action is to play the DVD/CD/MP3/recording directly from the original purchased version.
If you purchased a digital downloaded version, you need to play it from a legal source, such as the device you downloaded it to (your laptop or tablet) or a CD legally burned from it, or a flash (thumb) drive copy legally made.
If you need something from the web, link to it (or embed a player, if that's an option) rather than download it and convert the format for your own use.
YouTube (and other web videos)
YouTube videos (and many other videos on the web) are restricted by user agreements which must be consulted and observed.
YouTube and copyright law specifically FORBID converting videos for use in PowerPoint or other class use, whether by faculty or students.
See the YouTube Terms for details, including the specific agreement for everyone using YouTube:
Videos may only be linked, not converted, for use by faculty or students.
Using any method to change the file format of copyrighted digital material is forbidden by copyright law and there is NO Fair Use exemption.
Finding Content With Google
Google allows you to filter your search results to only show Creative Commons and public domain works. When doing an advanced search, you can choose which usage rights you want Google to search for. For example, if you're searching for an image to use in your blog, you can change the usage rights to free to use or share.
Use the Advanced Search in the upper left corner of the search results page, and filter your results.
THEN
The law allows you to do many things as a student, under "Fair Use", which are NOT legal once you are outside class. Much of the "free" material you can use for class work is NOT necessarily licensed for you to use commercially (in your job).
Be sure to doublecheck anything you use outside the classroom for copyright, so you -- and your boss -- don't violate copyright.
Just because it's visible on the Internet, does NOT mean it's free for anyone to use in any way.
Help is out there!