DualDisc was a type of double-sided optical disc product developed by a group of record companies including MJJ Productions Inc, EMI Music, Universal Music Group, Sony/BMG Music Entertainment, Warner Music Group, and 5.1 Entertainment Group and later under the aegis of the Recording Industry Association of America (RIAA). It featured an audio layer intended to be compatible with CD players (but not following the Red Book CD Specifications) on one side and a standard DVD layer on the other. In this respect it was similar to, but distinct from, the DVDplus developed in Europe by Dieter Dierks and covered by European patents.