Update: Google now offers a WebM plugin for Internet Explorer 9, much easier than what I’ve detailed below.
Google’s recent announcement deprecating H.264 for Chrome (see my thoughts on it) means it’s likely that WebM will become the defacto standard for the HTML5 video tag, supported by Internet Explorer 9. Unfortunately, Internet Explorer 9 does not (yet) ship with WebM, despite a lot of misleading PR indicating some kind of “compatibility”.
So, how do you play WebM with Internet Explorer 9?
The easiest way is to use the DirectShow filter pack from Xiph.org. Download and install the installer, available for both 32-bit and 64-bit Windows, and not only will you be able to play WebM/VP8, but also Ogg/Theora, Vorbis, Speex, and FLAC. It’s an royalty-free, open-source standards smörgåsbord!
What do you do next? Of course, submit feedback! Click Send Feedback under Internet Explorer’s Tools menu, and simply ask Microsoft: please support WebM!
Clarification: Don’t install the Support for HTML <video> tag option. It installs an ActiveX control, which requires some extra markup (see the release notes).
Note: Internet Explorer 9 is a beta, as well as Xiph’s DirectShow filters. IE9 doesn’t support a lot of <video> tag features, so many demos out there on the Internet don’t work.