MediaElement is a proposed interface for general-purpose imperative animation, patterned after HTMLMediaElement. SyntheticMediaElement is an implementation of this interface, aimed at library authors. If you've ever implemented a scrubber bar, this is for you!
In this post I'm going to explain my recent WICG proposal for [Synthetic]MediaElement, and go into more detail about some of the use cases. In short, MediaElement is a sub-interface of HTMLMediaElement—something which can be played/paused, has a currentTime, etc.—and SyntheticMediaElement is an implementation of MediaElement, not necessarily tied to the DOM. The goal is to preempt the spread of framework-specific animation plugins.