Goes though all available media sources until it finds one capable of constructing a GrlMedia object representing the media resource
exposed by uri.
This method is asynchronous.
| uri |
A URI that can be used to identify a media resource |
| keys |
List of metadata keys we want to obtain. |
| options |
options wanted for that operation |
| callback |
the user defined callback |
| user_data |
the user data to pass to the user callback |