Processor power and screen size are key inputs to coding decisions, says Mitch Dornich, Verizon’s director of product management and head of Verizon Video. The encoding methods match device and screen size to the encoding method and bandwidth. Verizon Tweaks Mobile Video Encoding
Where a device and screen cannot take advantage of the highest-possible resolution, the video is coded at less resolution. That has other benefits, of course. Users can avoid putting pressure on their data plan caps when video is sent only at rates that the device can display, or that the eye can detect.
That has become a bigger issue now that faster 4G networks are available, since delivering data at higher speeds also consumes a user’s “bucket of bits” faster.