Using a QAbstractUrlInterceptor subclass and installing it on your your QQmlEngine instance is advertised to allow you to modify urls as interpreted by the different components. It works fine for many things, like Image and SoundEffect. It does not work for MediaPlayer. The unmodified URL is passed on to GStreamer directly.

As even the documentation for QAbstractUrlInterceptor advertises how useful it is to use it to select "different graphical assets" I think it is reasonable to expect it work for all components taking urls for such things.