For video campaigns, a view means a view of the video (not an impression of the video player) and is sometimes called a play, to try and make this clearer.

We count a view after the video has started buffering and as soon as it starts playing. The user does not have to finish watching the video for the view to get counted.

For Eclipse campaigns, we count a view when the lightbox has expanded - so either after a user has clicked on the box, or after they have hovered over the box for three seconds. 

This way of counting views is in accordance with the IAB's definition of a commercial video impression, currently the only standard that exists, and it's the metric used by all the buyers and sellers of digital video advertising.