14. A non-transitory computer readable storage medium, having instructions stored therein, which when executed, cause a processing device to perform operations comprising: identifying a new media clip provided by a first user; providing a feature vector associated with the new media clip to a first classifier, wherein the feature vector associated with the new media clip includes a plurality of values representing one or more features extracted from content of the new media clip, wherein the first classifier was trained using a plurality of features vectors of a plurality of existing media clips to produce suggested semantic tags for respective existing media clips; obtaining, by processing device, a first set of semantic tags for the new media clip from the first classifier; providing, by the processing device, the first set of semantic tags for the new media clip to a second classifier that was trained using input-output pairs, wherein an input of each input-output pair includes a subset of the suggested semantic tags that was previously produced by the first classifier and suggested to a second user for one of the respective existing clips, and wherein an output of the input-output pair includes one or more suggested semantic tags selected by the second user from the subset of the suggested semantic tags for the one of the respective existing clips; obtaining, by the computer system, a second set of semantic tags for the new media clip from the second classifier; and suggesting to the first user, by the computer system, the second set of semantic tags for the new media clip.
14. A non-transitory computer readable storage medium, having instructions stored therein, which when executed, cause a processing device to perform operations comprising: identifying a new media clip provided by a first user; providing a feature vector associated with the new media clip to a first classifier, wherein the feature vector associated with the new media clip includes a plurality of values representing one or more features extracted from content of the new media clip, wherein the first classifier was trained using a plurality of features vectors of a plurality of existing media clips to produce suggested semantic tags for respective existing media clips; obtaining, by processing device, a first set of semantic tags for the new media clip from the first classifier; providing, by the processing device, the first set of semantic tags for the new media clip to a second classifier that was trained using input-output pairs, wherein an input of each input-output pair includes a subset of the suggested semantic tags that was previously produced by the first classifier and suggested to a second user for one of the respective existing clips, and wherein an output of the input-output pair includes one or more suggested semantic tags selected by the second user from the subset of the suggested semantic tags for the one of the respective existing clips; obtaining, by the computer system, a second set of semantic tags for the new media clip from the second classifier; and suggesting to the first user, by the computer system, the second set of semantic tags for the new media clip. 15. The non-transitory computer readable storage medium of claim 14 wherein the first classifier is trained for each of the suggested semantic tags using positive feature vector examples and negative feature vector examples, wherein the positive feature vector examples are feature vectors associated with existing media clips that have a corresponding tag, and the negative feature vector examples are feature vectors associated with existing media clips that do not have the corresponding tag.