The owner or the copyright is the only one who has the right to post the material on Youtube. The person posting a work may have the copyright owner's permission to post - as I said (above) is the case with some of the clips I posted (in addition to a Bill Staines song I posted a Michael Troy song). The others are either Public Domain or they are my songs.
There are a few clips of my performances that other people have posted on Youtube. They asked my permission first - I believe by law they only had to have permission for use of the song (not the performance).
I see many clips and many slide show or videos created by Youtube members that probably are made without the copyright owner's permission - but I suppose they'll stay until someone complains about infringement.
Murray - if you are not the composer of the song and someone points that out to Youtube, I suspect they'll pull your vids every time - possibly even close your account. If you are filming someone perform a public domain work in public - you're probably alright, even if the performer complains.
Youtube's funny - but they have everybody after them. It's their site. They make the rules. They feel if you want to use their site, you'll play by their rules.