Opera doesn’t support it; Firefox doesn’t support it; and now Chrome has announced that it’ll drop support for H.264 video codec for its <video> element, and will support only WebM (VP8) and Theora video codecs. Chrome was the only browser out of the top 5 to both support WebM and H.264 natively; Safari and Internet Explorer supports only H.264 codec.
There’s a turf war between H.264 and WebM to become the HTML5 <video> standard; H.264 has Internet Explorer’s and Safari’s support, while WebM has Chrome’s, Firefox’s and Opera’s. Of the two, H.264 is the more established codec, but suffers from unclear licensing terms which led to Google opensourcing WebM in order to provide the world with an opensource alternative.
As pointed out by some readers, the only clear winner in this turf war, is ironically, Adobe Flash; instead of being killed by HTML5 <video>, the turf wars have highlighted its strength as the only reliable medium for video streaming that can support both H.264 and WebM.