But think about it, what will happen then? You make it sound like this is a hypothetical scenario, but the codec mandate was removed from the HTML5 spec last J

But think about it, what will happen then? You make it sound like this is a hypothetical scenario, but the codec mandate was removed from the HTML5 spec last June. The reality is that Microsoft will support h.264, Apple supports h.264, Google supports h.264 (and Theora). Opera currently supports only Theora, but their implementation can support h.264. Mozilla is the only browser vendor that willfully forbids its users from viewing h.264 (or any other format but Theora) in <video>. In addition: Flash, Silverlight, and QuickTime all support h.264. Bear in mind that the <video> tag has always been codec agnostic and able to support multiple codecs in the same tag. The codec mandate was only to specify a common codec across all browsers, but there is no point in mandating something that won't be implemented.