We're sincerely sorry for being unable to download videos related to music category in 720p with sound. That's because YouTube recently made it restricted to download any video that is related to music due to its content policy. We're now working on this issue. We believe that we can get it solved soon.
However, you can download Music Videos in 720p and higher quality with VidPaw App on Android phone/tablets. If needed, you might as well give it a shot.