Oh that's the difference lol I got a video with music/live ultrasound. Def worth it!
The difference is that with 4D they give you a video of the Live ultrasound that shows all the movement and they add lullaby music to it, and the 3D pictures are way more vivid than 2D because you can see your babys features way clearer, I got it done and I loved it, it is very pricy but so worth it because I can have my daughter watch it when she's older :)
Mine was in 3d/4d and I didn't even notice the difference. You will def be able to see the baby and all the features.
I have no clue about a 4d but I do know the 3d is just that. 3D. A normal ultrasound is 2d and the features are not defined at all