Okay so here are all the hints I've given right next to each other. I think this should give it away, so if you want to find it yourself STOP reading!
1. The Annotation is in a Cuboid Video. (10 Cubiod videos)
2. The Annotation is in a Cuboid Video that I own two of. One that I bought and one that I made. (2 videos)
3. The Annotation is over a "magical puzzle"
4. The Annotation is shown for only 4 or 5 seconds.
Using these hints it shouldn't be too hard. As long as you understand #3.
Without giving it away, #3 should be obvious if you watched all of the videos.