As one who runs a specialist music site the placing of such a system on here would infringe against intellectual property rights if the correct fees have not been paid.
The USA in particular is continually having talks with China on this and those rights cover music as well.
If someone uploads to youtube any music even as background music, when they do not own the rights, then they will have adverts put onto the video which defray charges. In some cases where the owners of the rights have not agreed to this then youtube will remove the video from being viewed.
But running a music player without paying the fees could possibly end up with the site being closed down.
Even internet radio stations have to pay music fees.
Willy