The official codec for HTML5's video tag has been under debate ever since developers began adopting the new technology. A current standard, H.264 was a codec thought to be just perfect for use in the video tag, so perfect that Microsoft even announced Internet Explorer 9 will only support the codec for their HTML5 video tag. Google however has other plans for what codec will rise above the rest.
Google will begin phasing out H.264 support in Chrome over the next couple of months, Product Manager Mike Jazayeri writes on the Chromium Blog. Chrome will instead support their own codec, WebM (VP8), and the outside Theora codec as both are "completely open codec technologies." The changes made to Chrome in the next few months will allow for support of these codecs simply via the HTML5 video tag.
Reasoning behind removing H.264 from Chrome is that it, while playing "an important role in video," it is not truly an open codec like WebM or Theora technologies. H.264 was under fire last Fall for fears that people would be forced to pay royalties to use the codec. MPEG LA confirmed that H.264 will stay royalty-free to help create a standard for web video that all vendors could access with their mind at ease.
Google apparently is not satisfied enough, and only wishes to support truly open technologies as a goal of the company is to "enable open innovation." The search giant wishes to keep everything as open as possible, and with H.264 having patents owned by Microsoft and Apple, Google did not see that as fitting for their open web.