The live video stream is made available by the ISS HD Earth Viewing Experiment.
From The Telegraph:
NASA has launched a livestream of the earth from space, giving viewers the opportunity to see what only astronauts get to see.
Four HD cameras were attached to the International Space Station (ISS), which stream live video footage of the earth for viewing online.
[Our emphasis] The stream switches between the four cameras every few minutes, and occasionally dips into darkness during each orbit.
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From Universe Today:
Please note that the screen will appear black when the ISS is in orbital night — which happens every 90 minutes and lasts about 40 minutes.
…having live HD streaming views of Earth is pretty awesome – but it’s also nifty to note that this is part of a student project.
This experiment is completely separate from the UrtheCast [request an invite] commercial cameras on the ISS.
Black Image = International Space Station (ISS) is on the night side of the Earth.
Gray Image = Switching between cameras, or communications with the ISS is not available.
No Audio = Normal. There is no audio on purpose. Add your own soundtrack.