Vimeo writes in a blog post:
Since we rolled out the HTML5 player in January people have been clamoring for an embeddable version, especially for iPhones and iPads. Today we’re taking a big leap forward for compatibility and updating our embed code. We call it the Universal Player.
The Universal Player is as easy to use as the old embed code, just a lot more compatible. Instead of being a direct link to a Flash player the new Universal Player can automatically detect what kind of device is viewing the video and choose the optimum player based on the device’s capabilities. For example, it will serve mobile video to iPhones and Androids and HD to iPads and Desktops. On other mobile devices it can use the native player of the device or an optimized mobile Flash player with bigger controls. It also allows us to introduce new players as technology changes, potentially allowing us to do things like serve HTML5 to IE9 and WEBM video to Firefox.