[XeTeX] How does xetex handle non-native image files such as eps?

[Yuan Qi]

Ulrike Fischer <news2 at ...> writes:

> But don't forget: every non-native image file has to be converted by
> xdvipdmx during every compilation. This slows down compilation. So at my
> opinion it is better to convert the images before compilation in a
> native format.
> 

However, the on-the-fly conversion method is useful when dealing with images
 that are constantly being modified.

Does xetex support converting the image to PDF before compilation or is it only 
doable via a script.