3d sound in this context means when you turn your head the sound remains in the same '3d' position(so if the sound was coming from the side and you turn to face it, it now sound like it's coming from ahead), which is important for vr (with headphones). This isn't really possible with a prerecorded video file unless you have a clever player that can do the 3d transformations from the original sound channels, but I'm not aware of any that can do this yet