How I understand this is that backing tracks are still licensed, which makes sense as they are a part of the original recording. If the backing track is re-recorded by another person/band playing the instruments it is not licensed (I am not 100% sure of this, and I'm not giving legal advice), is like a cover song, so the karaoke type backing tracks are that. Backing tracks from the original recording will be recognized on Soundcloud, YT, FB, and SC used to block them. Youtube doesn't block or charge you, if you agree to have the music in your video attributed to the original artist, as it should be. For personal use and practicing, they are phenomenal to have. But you can learn them the old fashioned way, by playing along with the album, cassette, or CD and recording yourself with a "JamBox", lol. At least you can hear your mistakes, and keep practicing!