I have a few clips which I have downloaded from youtube. The quality is horrible, however. Is there any program out there which can improve the video quality?

Thanks for any advice.

You cannot add visual quality once visual data has been lost.
Imagine it this way, you have a book with a chapter missing - you could take a guess at what each page in the chapter discusses by knowing what comes before and after but you'd never be able to reconstruct the chapter word for word. It's exactly the same principle trying to increase quality in images after they have been compressed - you can get software which guesses at what data is missing but it's only ever going to interpolate between the data it can work from.
With youtube, the data you have left after compression is pretty useless to even interpolate from so you're never going to recover quality.

I watch a lot of TV. the CIA or FBI seems to be able to improve video quality. Las Vegas casinos also have that technology. But I don't believe it works for youtube vids

they don't improve video quality. At times they use software to ATTEMPT to guess what pixels would be added in between other ones, but it is very unreliable and does only one frame at a time. This would take forever for a video. They use it for individual frames to attempt to get a better look at people's faces.