Remaster Music Video's

I have a large collection of music video's downloaded from various sources (tut tut), the quality ranges from very poor to excellent.
Does anyone know if there is a downloadable program available which will basically 'remaster' my 'less than pristine' quality video's. Or is it the case that once poor quality vid's are downloaded the quality is therefore irreversible ?

 

You can't make a silk purse from a sow's ear.

Nothing can recreate the quality that is lost.

 

Yeah, I kinda thought something along those lines. I guess I was looking for conformation. Thanks for the reply.