Hey Tom,
This should be a relatively simple process for you.
Just ensure you aren't hiding the <video>tag behind a load of JavaScript and then reference the .mp4 version of the file in the <content_loc> element of your video sitemap, along side a thumbnail and other required metadata -http://support.google.com/webmasters/bin/answer.py?hl=en&answer=80472</content_loc></video>
However, in answer to your Q's, there are a couple of things you can do to make the rich snippets surefire
- You should also add the videoObject schema mark up (http://schema.org/VideoObject) before the <video>tag <div< span="">itemprop="video" itemscope itemtype="http://schema.org/VideoObject"></div<></video>
- If you're delivering both videos through the same player, i basically wouldn't worry about it and would just mark everything up to match the default (i assume) HD settings. Otherwise, i'd mark the two different versions as different schema.org videoObject's, using videoQuality and videoFrameSize to differentiate one as HD and one as SD. In your video sitemap, you should then include both videos under the same URL.
- Google claim they don't currently crawl Theora files. While this will certainly change going forward, i would for now just include the MP4 file in the video sitemap. What you include in the actual HTML probably wont matter, but safest bet will be to have the MP4 referenced.
Hope that's useful!
Phil