Player Framework is an open source video player framework for HTML5, Silverlight, Windows Phone and other application platforms. A comprehensive list of features including easy customization of the UI, plugin models, advertising standards support, W3C timed text (TTML) support for captions and more.
It offers a JavaScript API for controlling the player where the API methods are the same on both the HTML5 and Silverlight versions.

HTMl5 Video Player Framework Features
- JavaScript API for both the HTML5 video tag and the Silverlight player
- Pure JavaScript initialization by injecting the Player into a web page without pre-existing video or object tags.
- Accessible functionality through the use of alt and title tags and tabbable controls.
- Playlist support using an array of media items or using a link to a Media RSS feed.
- Closed Captions support using the TTML/DFXP specification
- Styleable controls
- Interactive timeline
- Volume control
- Mute control
- Full screen control
- Poster support
- Support for mobile platforms
- No other 3rd-party JavaScript libraries required
- Pre-load UI
- Error handling
Such a consistency is very handy for using any of the versions as a fallback of the other with almost no extra coding.
Website: http://playerframework.codeplex.com/
Demo: http://playerframework.codeplex.com/documentation