I was wondering about this:
What Live Photos do is save enough of these before-and-after photos to create a 1.5-second animation. It’s not video, it’s just effectively an animated GIF in JPEG format – a similar approach to Motion JPEG. Audio is recorded separately and then attached to the animation. The animations can be set as your iPhone wallpaper. Details of the file format were tweeted by Daniel Matte after speaking with an iPhone product manager, and are consistent with a brief description in Apple’s iOS Developer Library.
According to the link, Live Photos, though surprisingly compact, are still checking in at twice the size of a still photo, theoretically leaving you half as much room for Retina Flash-enhanced Live Selfies (yes, Live Photo works with the FaceTime camera) on your brand new 16GB Rose Gold iPhone 6s.