No they don’t: modern web browsers (read: all except Internet Explorer) support declarative SVG Animations, which rely on the SMIL/BasicAnimation module — hence the (common) confusion.
Web browsers don’t support the full SMIL recommendation, and they don’t support SMIL/Timing either. That’s what this project is about.
The SMIL spec is huge, it includes a specific box-model which is very far from the HTML/CSS one, and it’s only partially implemented by a few media players. It might be possible to implement SMIL in modern web browsers, too, but we think it would be inadequate:
SMIL has been designed for advanced synchronization tasks. Some SMIL aspects have already been ported to web standards (e.g. SVG animations and CSS transitions), our project is about porting SMIL/Timing and Timesheets to web documents.
effects if you don’t want to use the CSS
True: Microsoft started supporting HTML+TIME ten years ago with IE 5.5; but without SVG, <audio|video> elements and CSS transitions, there hasn’t been many real-life use cases so far.
We think it’s more than time to bring a modern, standard equivalent of HTML+Time to the web. Especially for multimedia-related tasks.