Video Tag
This plugin makes it easy to insert mp4 encoded HTML5 videos in a post. Octopress ships with javascripts which detect mp4 video support (using Modernizr) and automatically offer a flash player fallback.
Syntax
{% video url/to/video [width height] [url/to/poster] %}
Example
{% video http://s3.imathis.com/video/zero-to-fancy-buttons.mp4 640 320 http://s3.imathis.com/video/zero-to-fancy-buttons.png %}
You're probably using a browser which supports HTML5 video and you're looking at this page wondering if it really works. Reloading the page with the url hash #flash-test and you'll get to see the flash player fallback.