1. A video search assistant embodied in one or more machine readable storage media and accessible by a computing system to assist a user with a video search by: receiving a user-specified search request; determining a complex event of interest, based on the user-specified search request; accessing a video event model comprising a plurality of semantic elements associated with a plurality of complex events depicted in a plurality of videos, each of the semantic elements describing one or more of a scene, an action, an actor, and an object depicted in one or more of the videos; determining, based on the video event model, one or more semantic elements of interest associated with the complex event of interest; and formulating a search for one or more videos depicting the complex event of interest, the search comprising one or more of the semantic elements of interest.