Zencoder
Zencoder is the creator of an open-source HTML5 video player, Video.js, built with Javascript, HTML, and CSS. Video.js plays video via native playback in all HTML5 browsers and devices, or through Adobe Flash when HTML5 playback is not available.
Comparison of HTML5 and Flash
Tools for HTML5 are just starting to come to market; in the meantime, Adobe has released a first version of a Flash-to-HTML5 conversion tool for existing content and are working on creating new tooling for HTML5 as well, like Adobe Edge.