The number is the signature pixel density (PPI) for Apple's original Retina Display .
: Usually paired with AAC-LC audio up to 160 Kbps. 3. "Deep Text" and Research 326 mp4
: 326 pixels per inch (ppi) was chosen because, at a typical viewing distance, the human eye cannot distinguish individual pixels at this density. Primary Devices : This specification is foundational to: iPhone 4, 4S, 5, 5c, and 5s . iPad mini (2nd, 3rd, 4th, and 5th generations). 2. The "MP4" Connection: Video Support The number is the signature pixel density (PPI)