The AVC application, is an excellent tool for converting any type of video files.
However, what you really need is a dynamic media player that can play any type of media file, including flv, which is the output format used on youtube.
If you don't already have 'Winamp', more especially, the latest 5.54 player, which includes exciting new skins, you can download the FREE application at http://www.winamp.com/
Now all you need is an online solution for downloading your selection of videos.
Esnips is a popular file sharing community, of which I am a free member, you could be too, by signing up at http://www.esnips.com
Just for curiosity, I have just visited Esnips and made a search for "My little pony" video in the box (top right side). By clicking on 'download', it automatically downloads to my default Winamp player.
Guess what? I now have My little pony on my pc....thank you very much haha!
Incidentally, if ever Esnips have any copyright issues, and have to disable the download button for any particular file, there is a torrent site which can bypass the code, but I cannot write of that here - contact me if any probs!