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Hey Chris, it looks like you got some responses to this over on the Google Help Thread. This is an interesting question. My understanding is that you should include all relevant XHTML, image, and video elements within their corresponding <url>tag all within the XML sitemap itself</url>. This is discussed a little bit over at Allotment Digital and they even include an example XML file that shows the best practice writeup. Let me know if that's helpful or if you get any further clarification over on the Google thread.