Hi, I used a high quality youtube downloader to get some funny L4D videos, and the video output is mp4. Now I can't play them because "I don't have the retarded codec" so I go and download + install. Then, the video runs but it's just sound + visualization. I can't convert them, either. Help!

get the k-lite codec pack, has everything you need in my opinion

mpcstar is the best vid player out there, as far as i can tell. it's free, lightweight, includes pretty much every codec out there(from ogm-mkv), and it can even play partially downloaded files.