From nasa.gov: 

The High Definition Earth Viewing (HDEV) primary objective is to validate the space-based performance of the cameras in a variety of operating modes to exercise and demonstrate the features and longevity of the COTS equipment for future ISS Program usage. This payload is an external earth viewing multiple camera system using a set of Commercial-off-the-shelf (COTS) cameras. The HDEV integrated assembly is composed of a camera system of four COTS cameras, integrated Command and Data Handling (C&DH) avionics (ethernet), and a power data distribution box that allows the integration of the payload's components interface to the ISS Columbus module.

The HDEV visible HD video cameras are a fixed payload camera system that requires no zoom, no pan or tilt mechanisms. The four fixed cameras are positioned to capture imagery of the Earth’s surface and its limb as seen from the ISS (i.e., one camera forward pointed into the station’s velocity vector, two cameras aft (wake), and the other one camera pointing nadir). The video imagery is encoded into an Ethernet compatible format for transmission to the ground and further distribution. In this format, the video can be viewed from any computer connected to the internet.

The HDEV does not record video on board the ISS, all video is transmitted to the ground real time; any desired recording of the video occurs as ground operations. The COTS cameras, COTS encoder and other electronics are enclosed in a pressurized box to provide a level of protection to the electronics from the space environment. The Enclosure contains dry nitrogen at Atmospheric pressure.

The NASA High School Students United with NASA to Create Hardware (HUNCH) program participated in the development of the HDEV. The HDEV project partnered with the HUNCH program to build several structural and support components of the HDEV flight system.