You can safely download videos using VLC media player, it has this option buried within it's streaming features. This sometimes fails between step 3 and 4 and a scrolling error message appears rather than the video, I'm not sure why but VLC doesn't seem to like certain youtube URLs. This works for maybe 80% of videos on there.
1.open VLC media player
2."media"-->"open network stream"
3.input the URL of the youtube video
4.record it as it plays using the record button which can be made visible by going to "view"-->"advanced controls"
5. this makes an mkv file of the video, which will play perfectly in vlc but other media players might struggle with, you will then need to go through a trial and error conversion process to find a good set of conversion settings if you want to play it in other programs.
You can also try youtube video downloading websites, where you input the URL of the youtube video, the site does "something" and then serves you up a download of an avi, mp4, mpg, mkv, ogg, mov, wmv, asf, mpeg, file of the video, but many of these sites are loaded with adverts and some might try and encourage you to download "toolbars" or "download managers" which are likely to be malware.
The third solution is browser add-ons (especially for firefox) which can download the videos for you, once again: some of these are safe, other's aren't, it's not always easy to tell which are which.
For the purposes of re-posting the youtube videos elsewhere, you really shouldn't. If the video's creator said in his description that he is fine with people sharing and downloading the clips then it's fine enough to download them to your hard-drive for personal private non-commercial use but reuploading them elsewhere is probably not what the original video poster wanted. You should respect the wishes of the video creator first and foremost and when sharing the video with others just give them it's youtube link. I can see why people want to download videos for personal offline use (you might want to be able to watch it on a laptop whilst you are somewhere without good connectivity, or you might want to save your internet bandwidth on something you regularly view by downloading once rather than playing many times, or you might just want to "have" it where you can keep a copy on your harddrive) but for sharing your best option realy is just to give people the link and tell them to run an ad-blocker.
The whole of this response also goes towards the other recently opened thread on here about downloading youtube videos.http://www.bleepingcomputer.com/forums/t/567874/extracting-underlying-link-from-youtube-videos/
Edited by rp88, 25 February 2015 - 12:36 PM.
Back on this site, for a while anyway, been so busy the last year.
My systems:2 laptops, intel i3 processors, windows 8.1 installed on the hard-drive and linux mint 17.3 MATE installed to USB