1. A computer-implemented method for annotating videos with entities and associated probabilities of existence of the entities within video frames, the method comprising: selecting an entity from a plurality of entities identifying characteristics of a video item, the video item having associated metadata; receiving probabilities of existence of the entity in video frames of the video item; selecting a video frame determined to comprise the entity responsive to determining the video frame having a probability of existence of the entity greater than zero; determining a scaling factor for the probability of existence of the entity using the metadata of the video item; determining an adjusted probability of existence of the entity by using the scaling factor to adjust the probability of existence of the entity; and labeling the video frame with the adjusted probability of existence.