The third release of the Internet Explorer 9 Platform Preview arrived today. The new version brings long-awaited support for HTML5 <video> and <audio> elements, 2D graphics using the <canvas> element, and support for embedded fonts using the WOFF standard. To top it all off, Platform Preview 3 also updates the Internet Explorer's new Chakra JavaScript engine to support the recent ECMAScript 5 specification.

Video tags enable sites to offer YouTube-like video without a dependence on proprietary plugins like Adobe's Flash or Microsoft's own Silverlight. With support now found in Firefox, Chrome, Safari, and Opera, Internet Explorer is the odd man out, a flaw that Internet Explorer 9 seeks to remedy.

That video support was included in Platform Preview 3 is no surprise; support for HTML5 video in Internet Explorer 9 was promised back in March at Microsoft's MIX event, and the company confirmed that support would be included in the third preview when it released Platform Preview 2 back in May.

WOFF font support is also no surprise, as it was promised back in April. With WOFF fonts, Web developers have a reliable, standard mechanism for using custom fonts in webpages, which enables richer, more varied designs. Prior to support for embeddable fonts, developers wanting to use custom fonts had little option other than to embed static images of text—which are annoying to edit and invisible to search engines and accessibility software—or resort to clever JavaScript trickery.

What does come as a surprise is canvas support. Microsoft has been promoting Internet Explorer 9's support of SVG, which provides vector graphics capabilities within the Web browser, but thus far has kept quiet when asked if it would support the canvas bitmap graphics specification. Not only is canvas being supported, it is also being hardware accelerated, continuing Microsoft's efforts to give Web applications the ability to exploit the extensive hardware capabilities of modern PCs.

As with previous Platform Preview releases, Microsoft's IE Test Drive site includes a set of new demos to show off the features of the latest release, along with many dozens of new individual tests for specific features. Continuing Redmond's test development policy, these tests are being submitted to W3C for inclusion in the standards body's test suite.

The new features give a healthy boost to Internet Explorer 9's score on the infamous Acid 3 test; it leaps from 68 in Platform Preview 2 to a rather more respectable 83. Though still some way behind the market leaders, the third preview does fill out most of the major gaps, making it a much more rounded release.

HTML5 video will contain built-in support only for H.264. Google's recently-opened WebM video format will work in Internet Explorer 9, but only if a suitable codec is manually installed. This is a bit of a problem, though, because although Google has published a codec for Windows' older DirectShow framework, Internet Explorer 9 demands codecs using the newer Media Foundation framework.

The big question with Internet Explorer 9 remains unanswered: when will this thing actually ship? The current versions of the other major browsers already have good HTML5 support. Safari has some amount of hardware acceleration already, and similar capabilities are likely to ship with Firefox 4 later in the year.

The Internet Explorer 9 previews certainly show that Microsoft is serious about its commitment to supporting HTML5, but that's only half the story. Developers can't exploit these new features until they're in end-users' hands. When that might be is still, unfortunately, anyone's guess.