You may have seen this 12 minute demo of Metal Gear Solid V: Ground Zeroes, but most likely you watched it with Kojima warbling over it in Japanese. As much as I love to listen to Kojima warble, my Japanese is fairly rudimentary. This 12 minute video has all the content seen previously, but this time the commentary is in English, which is helpful for us monolingual savages.
This video is also helpful in the context of some clarifications from Kojima and company. Metal Gear Solid V: Ground Zeroes is a stand alone prequel — shorter, cheaper, more concise — that exists as a sort of introduction to the expanded gameplay we're going to see in Metal Gear Solid V: The Phantom Pain.