Valid 'Episode Asset URL Template' Variables

I’ve looked in the documentation for a list of valid variables that can be used for this field but have failed to find anything. If such a list exists, perhaps a link to it can be provided under this field?

All of my episodes are in the format 0001-episode-slug and I’m trying to adjust the URL Template accordingly.

%media_file_base_url%%episode_number%-%episode_slug%%suffix%.%format_extension%

This doesn’t work however, I’d expect an %episode_number% and perhaps %episode_number_padded% to be available, is this not the case?