Analytics will count it a One (‘1’ )Unique Event, even if a user watches a video with event tracking three times but in a single session.
The correct answer is: 1
If a user watches a video with event tracking, three times in a single session, Analytics will count it just 1 unique event. Unique Events are interactions with content by a single user within a single session that can be tracked separately from pageviews or screen views. Downloads, mobile ad clicks, video plays, and interactions with gadgets, Flash elements, and AJAX embedded elements are all examples of interactions you might want to track as Unique Events.
Analytics increments the Unique Events metric by 1 the first time during a session that it receives an event with a unique combination of Category/Action/Label, and ignores subsequent events in the session that have the same combination of Category/Action/Label.