Since we have concluded video is important for your overall search efforts, I figured I follow up about a recent thread I spotted at Google Groups about the question on if Google supports MRSS as a format for Video Sitemaps.
The quick answer is yes, but it is not so clear from their documentation. MRSS, which is Media RSS, is one of the two formats Google seems to accept. I submitted an MRSS feed as a test and it did realize and label the feed as MRSS, but my feed did have some errors.
Googler, JohnMu, explained in the thread:
Yes, we do support mRSS for video Sitemaps. It's not explicitly mentioned, which may cause some confusion (we'll fix that :-) - thanks for bringing it up).
What you can do is the following: Just submit your mRSS file as a normal Video Sitemap in Webmaster Tools. Once we start processing it, you should see the mRSS information in the Sitemaps information page in Webmaster Tools to confirm that we're processing it correctly.
So if you have a video sitemap in MRSS format that you already publish, it might be worth trying to submit that to Google as well.
Forum discussion at Google Groups.