Speculation continues after the jump.
We take this to mean that Bay's prepping some "never-before-seen" footage to be included on the DVD, which will help set up the storyline he plans to follow for the sequel. There's all kinds of stuff he can do, as (mild spoiler alert) Bumblebee is the only 'bot whose arrival we don't see happen in the film. As the Autobot doing recon for the others, Bay can show us how he came to arrive on Earth, turn into the beater Camaro, find Sam, and provide other new plot tidbits that will be revisited in the sequel. (FYI, plot spoiler coming in next sentence.) Since Ryan says he's recorded new material for the DVD, however, it probably means that the prequel stuff he did involves the pre-Bumblebee-on-Earth timeframe, as in the film, Bumblebee does not have a voice until the conclusion of the film. Until then, he communicates with Sam and the other Autobots via the Camaro's car stereo because his voice was damaged in an earlier off-screen battle with the Decepticons. This is just us speculating, of course. We don't know what the disc (or discs) will hold, but from the sound of things, theres going to be some juicy new stuff to see.