I use Unity to create augmented reality app via vuforia, I want to replace the 3D object above the image target by playing a video playback. how can I do that?
unity3d - Put Video Above the Image Target in Android AR
I'm not sure if I understood you so I'm gonna give the 2 possibilities.
If you want to play a video instead of the 3dModel :
you can drag a Gameobject -- ex : plane with a MovieTexture) -- under you ImageTarget.
Or if you to play a video behind you 3DModel then :
On the ARCamera/WebcamBehavior : you can disable the "Playmode render video". the AR function will still trigger but you dont have the webcam render on the background. so you're free to playback whatever you want on the back.
now you are free to put what ever you want behind.