the metadata can only contain a url or some text file, you can use this url to add stuff or augmentations to your project, for example, to display a 3D object, you should use a .obj parser, as unity cannot create 3D objects at runtime unless you use asset bundles, and for that the asset bundle must be built inside the unity editor itself and then uploaded. I would recommend you have a .txt file with just the url of the .obj and its texture, save the contents of the url to a text file in your application persistent path, then run the .obj parser to generate a mesh at runtime. As for running videos, just use unity's videoplayer with audio source to play from url or use easy Ar's prefab to achieve the same.