If you don't have a license, you can't legally offer the file to download, unless it is shared with one of a select number of free licenses that don't require attribution. A "thanks" is no legal protection against DCMA takedown notices and RIAA or MPAA lawsuits.

So in short: you need licenses.

If it's not your content (especially if it's music videos) and you are letting people download them (worse if you are profiting from it) you will probably get in trouble with those who actually own the content.