This has probably been asked several times and most people (including myself) have downloaded programs to do this with varying success. I've just come across this method which doesn't involve installing any software and gives you different formats for saving:-
(Courtesy of PCMech.com)
Whenever you are watching YouTube videos you probably come across some that you would like to save to your hard drive. While there are software titles and browser plugins which will do this for you, the abosolute easiest way I have found is by using KickYouTube.
KickYouTube requires no software installation or registration of any kind and the usage could not be easier. There is a walkthrough on their main page, but basically all you do is this:
1. Go to the video you want to download on YouTube's site.
2. Change the URL at the top by adding "kick" in front of youtube.com. For example
https://www.youtube.com/watch/?v=12345 becomes
http://www.kickyoutube.com/watch/?v=12345 3. You will be taken to KickYouTube's site.
4. Select your download format from the top bar and click download.
5. That's it.
Again, there is no software required or account to create so enjoy!