Can I add external links to my sitemap?

[SEOdub]

Hi,

I'm integrating with a service that adds 3rd-party images/videos (owned by them, hosted on their server) to my site. For instance, the service might have tons of pictures/videos of cars; and then when I integrate, I can show my users these pictures/videos about cars I might be selling.

But I'm wondering how to build out the sitemap--I would like to include reference to these images/videos, so Google knows I'm using lots of multimedia. How's the most white-hat way to do that? Can I add external links to my sitemap pointing to these images/videos hosted on a different server, or is that frowned upon?

Thanks in advance.

[Tenlo]

The point of a sitemap is to tell Google what is on your site so it can index it easier. There is no way, nor any reason why you would want to put external urls onto your sitemap.