combine.swift

//this takes a list of items in an array, then runs an observable on each of them, finally it combines
//all of the outputs into one observable which returns all of the media items at once

Observable.combineLatest(mediaItems.map({ $0.getMediaMetadataObservable() })).subscribe(onNext: { a in
      for item in a {
        print (item.type)
      }
})