Comment 7 for bug 153054

I don't think it's necessary to store such an ID for every song.

You should go for a configuration setting with which the user can indicate which directiories contain dynamic content. If a file in such a location is attempted to be played, you need to check and store in the back if the given location contains files at all (is mounted or not). After that, you can automatically mark every file under the given path as "temporarely not available" in it's display logic and simply don't attempt to play files below this location anymore.

I'd suggest to have a little background task running which checks every X seconds if a location that is marked as dynamic is available to correctly mark the songs while displaying. If a file is not available, but it's dynamic location is marked "mounted", you can asume it has been deleted.

This way of realization also allows you to mark parts of a library as dynamic.

If you go a step further, you could ask DBus about the info instead of simply checking that a dynamic location is empty (not mounted).

HTH!