It is basically illegal to provide copyrighted material without the consent of the copyright holder.
So DVDs released "officially" (in this case by Queen Productions Limited) is protected by the copyright, and cannot be re-sold or re-distributed in a mass market manner (as posting it on this site would be).
Reselling your own personal copy of a DVD or CD (i.e. at a car boot sale or on Amazon second hand or on eBay) is, I believe, legal as you are reselling the original product. If you copied that product and sold that copy, that would be illegal.
So that is the dilemma. If something is a "bootleg" (i.e. hasn't been officially released) then it can be posted and enjoyed by all. You just need to know what's official and what's not. Not always easy.
Tatterdemalion and the junketer
There's a thief and a dragonfly trumpeter