[Mauzen]

Downloading it is ok for 99% of all videos, but uploading it again might be a problem. Best thing would be to ask the original owner of the video for his permission, then you are safe. Else ******* might lock the video automatically, or the owner asks you to remove it. There wont be further legal consequences I think.
But in fact uploading the (copyrighted) music without the expicit permission is illegal.