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.
MuseScore
MuseScore.com allows playback of a score in any browser supporting the HTML5 audio tag. A score can also be linked to an online video, so that one may follow the sheet music while watching a video featuring that score.