About the ISS HD Views Channel
The High Definition Earth Viewing (HDEV) experiment aboard the ISS was activated April 30, 2014. It is mounted on the External Payload Facility of the European Space Agency’s Columbus module. This experiment includes several commercial HD video cameras aimed at the earth which are enclosed in a pressurized and temperature controlled housing. Video from these cameras is streamed 24/7, though there isn't always a discernable picture. Some quick notes:
Black Image = The view is switching between cameras or the space station is above the night side of the Earth.
Gray Image = Switching between cameras, or communications with the ISS are not available.
No Audio = There are numerous, sometimes extended periods when the station cannot communicate with mission control, or when the crew and ground controllers simply don't need to talk.