The number is the signature pixel density (PPI) for Apple's original Retina Display .
The standard video format for these 326 ppi devices is . 326 mp4
: Apple provides "deep" documentation on iPhone 5c and iPhone 4 specs, covering everything from the 326 ppi display to MP4 playback limits. The number is the signature pixel density (PPI)
: For older 326 ppi devices (like iPhone 5c), the standard was H.264 video up to 1080p at 30 frames per second . : For older 326 ppi devices (like iPhone
: 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
If your query refers to technical research rather than hardware: