HTML5 video is fairly mundane at this point, but that doesn't mean it can't get any new features. The latest Firefox 20 Nightlies have gotten support for custom playback rates, making it possible to slow down or speed up the video.
Also new is support for the <a> "download" attribute, one of the more recent additions to the venerable link.
The custom HTML5 video playback rate makes it possible to do more with video straight from the browser, without any additional effort. There aren't that many use cases for a custom playback rate, but it could be useful.
The HTML5 YouTube video player, for example, allows users to control the playback rate.
Another new capability in Firefox is support for the HTML5 "download" attribute. As the name suggests, it's used to indicate that the content pointed at by a link is downloadable.
A simple example is an image, instead of having the browser display it as would be the default, it should download it. It's even more useful with data blobs, i.e. data created inside an app that needs to be exported/downloaded.