Brian Deitte (one of our senior Flex engineers, and former Allaire/Macromedia/Adobe graduate) has a nice post on his explorations with BEML, our markup language for creating custom video player experiences.
BEML (stands for Brightcove Experience Markup Language) is a light-weight markup language that is loosely based on XUL (the UI layout engine that sits behind Firefox's UI). We've taken the core layout language and expanded it with the notion of Modules and Components, both of which can be authored using Flash ActionScript 3 APIs. We include a wide range of built-in components, but also there are dozens of 3rd parties building plug-in components for everything from video ad networks, to new video recommendation engines, to sub-titling tools, to advanced analytics plug-ins.
This broader openness is a hallmark of what we're trying to build at Brightcove -- a platform-as-a-service for rich media content on the Web.