10. The system of claim 9 , wherein the computer processor is further configured to train the set of initial classifiers, the set of initial classifiers including a first initial classifier trained using a first initial positive training set comprising co-watched videos with a group of authoritatively labeled videos, and a second initial classifier trained using a second initial positive training set comprising search videos and the group of authoritatively labeled videos.
9. The system of claim 7 , wherein each video is associated with a feature vector determined by a set of initial classifiers, and training the unified classifier based on the plurality of positive bags and plurality of negative bags comprises training the unified classifier based on the feature vectors associated with the videos in the plurality of positive bags and the plurality of negative bags.