Safari 4.0.5 will not play any HTML5 (H.264) video

The html5test.com tells me that my browser does not support the <video> element, and when I try example page, I get the fallback message, usually "Your browser does not support HTML5 video."

I know this should work in Safari. I am on开发者_高级运维 Windows 7, 64-bit (running 32-bit Safari).

Video works in Safari for everyone else in the office. (Windows 7 setup exactly like mine, Vista, OSX.)

I have tries uninstalling, deleting all user preferences, and reinstalling. Anything else I should try?

HTML 5 support did not make it into Safari until version 5. (Reference.) Upgrade to 5.