Those with HD-capable webcams, a little oomph in bandwidth, and more processing power will get the chance to broadcast their Hangouts on Air in HD as Google begins rolling it out in the next few weeks. Hangouts on Air is the live-streamed version of Hangouts, where anyone with a Google+ account can watch. According to GigaOM, YouTube has switched from the H.264 video codec to their own VP8, an open and royalty-free codec. H.264 just uses too much processing power to allow lots of people stream in HD. However, H.264 will continue to run on mobile devices.
Up next in the future of Hangouts on Air is WebRTC, which would allow users to chat without plugins. But one of the reasons why it hasn't been implemented yet is because of the silly features like birthday hats that people like to add to the picture that require facial recognition software to execute. WebRTC will likely be the future in the next few months as they iron out all those little issues.
So, some of you will already be able to stream 720p video with Hangouts on Air. Like anything Google does, not everyone will see it right away. It will be available to all who have the capability within a few weeks.