1. A computer-implemented method for annotating a digital video stored in a video repository, the method comprising: identifying a visual object displayed within the video using visual object recognition; determining whether a user, who did not contribute the digital video to the video repository, is authorized to annotate the digital video; responsive to the user being authorized to annotate the digital video, providing to the user a first web-based user interface portion for annotating the digital video, the first web-based user interface portion comprising visual representations of a plurality of different annotation types and a visual suggestion to annotate the visual object; responsive to receiving a user selection of one of the annotation types and approval of the suggestion of annotating the visual object, providing to the user a second web-based user interface portion comprising at least one input area for specifying a URL for a new annotation for the visual object, the URL separately encoding both an identifier of a target video and a time stamp of a moment within the target video; receiving a request from the user via the second user interface portion to add an annotation of the selected annotation type to the visual object, the request comprising a designation of the URL for the annotation; tracking a spatial position of the visual object across frames of the video to identify a plurality of spatial positions of the visual object as the visual object moves within the video; and adding the annotation to the digital video such that the annotation is displayed during playback of the digital video and moves responsive to the tracked plurality of spatial positions of the visual object, and such that selection of the annotation causes playback of the target video at the moment in the target video specified by the time stamp, the target video being different than the digital video.