As the Developer Terms of Service state, an app utilizing Spotify Services / Content may not synchronize music to "visual media", such as videos and slideshows. So obviously, things like adding a soundtrack to a movie are out of the question.
What I am unsure about is at what point something becomes synchronization to "visual media". This app (https://developer.spotify.com/community/showcase/3d-music-maze/) featured on Spotify's community showcase has the user move around a 3D maze made of album art, and when you bump into or click on different album art, a song from that album plays. I'm interested in this idea of looking at things with different songs associated with each of those things, but to me that seems like synchronization with what the user is viewing, like a soundtrack to a game or slideshow.
Can someone point me to a more in-depth resource that explains what counts as synchronization of music, or explain why this app doesn't violate the Terms of Service? Does it have to do with the fact that the music playing is controlled by the user's actions, instead of it being a timed sequence that you hit "play" on and sit back?